Dual criminality is the single most overlooked defense in extradition law. Governments requesting surrender must prove that the alleged conduct amounts to a criminal offence in both countries. If it does not, extradition is impossible. Full stop. Yet most people facing an extradition request never even consider whether this principle applies to their case.
The rule sounds dead simple: if the act is not a crime where you are, they cannot take you to where it is. But the reality is far more complicated. Courts across the world interpret dual criminality differently. Some apply it strictly, comparing specific statutory offences. Others take a broader “conduct-based” approach that gives requesting states far more room to manoeuvre. And certain frameworks, like the European Arrest Warrant, have carved out exceptions that bypass the requirement entirely for dozens of offence categories.
I’ve seen this play out before. A client charged under a US federal statute that has no equivalent anywhere else in the world. A European warrant issued for conduct that barely qualifies as a regulatory infraction in the requested state. A government stretching the definition of “equivalent conduct” until it snaps. The double criminality principle sits at the heart of every one of these fights.
This guide breaks down how dual criminality actually works in practice, which jurisdictions enforce it strictly, where the exceptions lie, and what landmark cases have shaped the law. Whether you are facing a UK-US extradition request or a warrant from an EU member state, understanding this principle could be the difference between surrender and discharge.
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Book a Strategy Call with RichardWhat Is Dual Criminality in Extradition Law?
Dual criminality (also called double criminality) is a foundational principle of international extradition law. It requires that the conduct underlying an extradition request must constitute a criminal offence in both the requesting state and the requested state. If the alleged behaviour is only illegal in one country, no extradition can proceed.
Think of it as a basic fairness check. A country should not hand over a person to face prosecution for something that is perfectly legal on its own soil. Without this safeguard, any state with broad criminal statutes could reach across borders to prosecute conduct that the rest of the world considers lawful.
The principle traces back to the Jay Treaty of 1794 between the United States and Great Britain. That agreement included what legal scholars now call the “Jay proviso,” a procedural requirement that the requesting state produce sufficient evidence of criminality. Over the next two centuries, through interaction between common law and civil law systems, this evolved into the substantive requirement we know today: the acts themselves must be criminal under both legal systems.
Under UK law, Section 64 of the Extradition Act 2003 establishes the double criminality requirement for Part 1 (category 1) extradition requests. The conduct described in the warrant must amount to an offence under the law of the relevant part of the United Kingdom, punishable by imprisonment of at least 12 months, if that conduct had occurred within its territory.
Here’s what most people miss. Courts do not typically compare the exact wording of criminal statutes side by side. The test is whether the underlying conduct, transposed into the requested state, would constitute a crime there. This “conduct-based” approach gives requesting states more flexibility, but it also creates genuine defense opportunities when the conduct simply does not map onto any local offence.
How Dual Criminality Works: The Two Main Tests
Not every country applies the principle the same way. Two distinct approaches have emerged across common law and civil law jurisdictions, and understanding the difference matters enormously when building a defense.
The Conduct-Based Test
Most modern extradition treaties and statutes use a conduct-based test. The court asks a straightforward question: if the alleged conduct had taken place in our jurisdiction, would it amount to a criminal offence here? The specific name of the offence, the statutory framework, and even the precise legal elements do not need to match. What matters is the behaviour itself.
The UK Supreme Court confirmed this approach in the landmark 2025 decision of El-Khouri v Government of the United States of America [2025] UKSC 3. The Court held that “conduct” should be given its ordinary meaning, focusing on where the physical acts were done, not where effects of those acts were felt. This ruling quashed an extradition order and sent a clear message: courts must look at what the person actually did, not how creatively the requesting state characterises it.
The Offence-Based Test
Some older treaties and a handful of civil law jurisdictions still apply an offence-based test. This stricter approach requires that the specific criminal offence charged in the requesting state has a direct equivalent in the requested state. If Country A charges someone with “wire fraud” and Country B has no offence by that name or close equivalent, extradition fails.
The offence-based test is increasingly rare. But where it applies, it creates a much higher barrier for requesting states and, correspondingly, a much stronger shield for the person sought.
| Feature | Conduct-Based Test | Offence-Based Test |
|---|---|---|
| Focus | Underlying behaviour | Specific legal charge |
| Statutory name match required? | No | Yes |
| Prevalence | Most modern treaties and statutes | Older treaties, some civil law states |
| Flexibility for requesting state | Higher | Lower |
| Defense opportunity | Moderate (focus on conduct gaps) | Strong (focus on offence gaps) |
| UK position | Primary test under EA 2003 | Not used |
| US position | Primary test (Collins v Loisel standard) | Rarely applied |
Dual Criminality Under UK Law
The United Kingdom applies the double criminality rule through two parallel frameworks, depending on which “Part” of the Extradition Act 2003 governs the request.
Part 1: Category 1 Territories (Previously EAW States)
Section 64 of the Extradition Act 2003 governs the double criminality requirement for Part 1 requests. The conduct described in the warrant must be punishable by at least 12 months’ imprisonment in both jurisdictions. Before Brexit, the European Arrest Warrant framework allowed EU member states to bypass this requirement for 32 categories of offences. That exception no longer applies to UK extradition proceedings where the arrest took place after 31 December 2020.
This is a significant shift. Post-Brexit, every extradition request reaching a UK court from a former EAW state must satisfy the double criminality test. No exceptions. That window has closed.
Part 2: Category 2 Territories (Including the US)
Section 137 governs Part 2 requests, including those from the United States under the UK-US Extradition Treaty 2003. The test is functionally identical: the conduct must amount to an offence in the relevant part of the UK, carrying a maximum penalty of at least 12 months’ imprisonment.
The 2025 El-Khouri decision reshaped how UK courts apply this test to US requests. The Supreme Court ruled that where the physical conduct occurred matters. You cannot artificially transplant “effects” of conduct into UK territory to manufacture jurisdiction. For anyone facing a UK-US extradition, this ruling is a wake-up call for the prosecution and a lifeline for the defence.
Dual Criminality Under US Law
American extradition law approaches the double criminality requirement through its treaty obligations and federal statute. Under 18 U.S.C. § 3184, extradition from the United States can only proceed pursuant to a treaty. And virtually every US extradition treaty in force today requires double criminality.
The foundational US standard comes from the Supreme Court’s 1922 decision in Collins v Loisel (259 U.S. 309). The Court held that the requirement is satisfied if the particular act charged is criminal in both jurisdictions. American courts do not require that the offence carry the same name or fall under the same legal category. The question is whether the underlying conduct is punishable in both places.
But here’s where it gets interesting. The United States has several uniquely American criminal statutes that create real double criminality problems when it seeks extradition from abroad.
RICO and CCE: The American Exceptions
The Racketeer Influenced and Corrupt Organizations Act (RICO, 18 U.S.C. §§ 1961-1968) and the Continuing Criminal Enterprise statute (CCE, 21 U.S.C. § 848) are uniquely American constructs. No other country has identical legislation. On paper, this should make extradition impossible for standalone RICO or CCE charges.
In practice, US prosecutors have found workarounds. They argue that the underlying predicate acts (fraud, drug trafficking, money laundering) satisfy the requirement even if the RICO “enterprise” charge itself does not. Courts have sometimes accepted this reasoning, but the argument remains contested. The Department of Justice’s own guidance acknowledges that pure RICO and CCE charges create double criminality complications in extradition proceedings.
The European Arrest Warrant and Dual Criminality Exceptions
No discussion of the double criminality rule is complete without addressing the European Arrest Warrant (EAW). The EAW framework, established by Council Framework Decision 2002/584/JHA, created the most significant exception to the principle in modern extradition law.
Article 2(2) of the Framework Decision lists 32 categories of offences for which the executing member state cannot refuse surrender on double criminality grounds, provided the offence carries a maximum sentence of at least three years in the issuing state. These categories include terrorism, human trafficking, corruption, fraud, money laundering, cybercrime, murder, kidnapping, and organised crime, among others.
Let’s be blunt: this is a massive carve-out. For these 32 offence types, a member state can issue an EAW and the executing state must surrender the person without checking whether the conduct is also criminal under its own laws. The only requirement is that the issuing state classifies the offence within one of the listed categories and that the sentencing threshold is met.
| EAW Framework List Category | Dual Criminality Check Required? | Minimum Sentence Threshold |
|---|---|---|
| Terrorism | No | 3 years |
| Human trafficking | No | 3 years |
| Corruption | No | 3 years |
| Fraud (including EU financial interests) | No | 3 years |
| Money laundering | No | 3 years |
| Cybercrime | No | 3 years |
| Murder, grievous bodily injury | No | 3 years |
| Organised crime / racketeering | No | 3 years |
| Drug trafficking | No | 3 years |
| Arms trafficking | No | 3 years |
| Environmental crime | No | 3 years |
| Offences outside the 32 categories | Yes | 12 months |
For offences that fall outside the 32 listed categories, Article 2(4) allows member states to require dual criminality. Many do. So if the alleged conduct does not fit neatly into one of the framework list categories, the traditional double criminality defense remains very much alive within the EU system.
The Extradition Report includes a full breakdown of how the EAW framework interacts with double criminality defenses across every EU member state.
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Get The Extradition Report NowLandmark Cases That Shaped Dual Criminality Law
Case law is where the principle moves from theory into real outcomes. These decisions define the boundaries of the principle and reveal exactly how far courts will stretch it, or refuse to.
Norris v Government of the United States [2008] UKHL 16
Ian Norris was indicted in Pennsylvania on charges of price-fixing in the carbon products industry. The alleged cartel operated from 1989 to 2000. The problem? During that entire period, mere price-fixing (without aggravating features like fraud or deception) was not a criminal offence in the United Kingdom. It only became one under the Enterprise Act 2002, which took effect in 2003.
The House of Lords allowed Norris’s appeal on the price-fixing count. The conduct alleged, stripped of any aggravating features, simply did not amount to a crime in the UK at the relevant time. Dual criminality was not satisfied. No extradition on that charge.
The case is a textbook example of the principle working exactly as intended. Norris was not discharged entirely (obstruction of justice charges survived the challenge), but the core price-fixing count fell away because the law in the requested state did not criminalise that specific behaviour.
El-Khouri v Government of the United States [2025] UKSC 3
This is the most important double criminality ruling in recent years. The US sought El-Khouri’s extradition for allegedly paying a middleman to obtain inside information about major M&A deals, then trading on that information using contracts for difference.
The Supreme Court quashed the extradition order. The ruling clarified that when applying the dual criminality test, courts must focus on where the physical acts were done. The word “conduct” means what it ordinarily means: the actual behaviour of the person. Courts cannot transplant the effects of that conduct into UK territory to create jurisdiction that does not otherwise exist.
For anyone facing US extradition through the UK, this decision is a game-changer. It reins in the broad interpretive approach that lower courts had been applying and places a meaningful check on jurisdictional overreach by requesting states.
Robert Spring (Ontario Court of Appeal, 2005)
A US citizen charged with illegal arms sales was denied extradition from Canada. The court found that the equivalent acts, under similar circumstances, were not considered a crime under Canadian law. The double criminality requirement was not met, and extradition was refused.
Collins v Loisel, 259 U.S. 309 (1922)
The US Supreme Court established that the requirement is satisfied when the particular act charged is criminal in both jurisdictions. The Court rejected the notion that the offences must be identical in name or classification. This “conduct” approach has remained the governing standard in American extradition law for over a century.
When Dual Criminality Makes Extradition Impossible
There are specific scenarios where the principle acts as an absolute bar to extradition. Governments do not play fair when they want someone badly enough, but certain factual patterns make extradition impossible to sustain on legal grounds.
Conduct Legal in the Requested State
The most straightforward scenario. If the conduct alleged is perfectly lawful in the country where the person is located, the test fails. Cannabis-related offences illustrate this well. A person charged with cannabis distribution in a US federal court cannot easily be extradited from a jurisdiction where cannabis is fully legal and regulated, because the underlying conduct does not constitute a crime there.
Uniquely Domestic Offences
Some criminal statutes exist only in one country’s legal system. US RICO and CCE charges are the classic examples, but they are not the only ones. Tax offences structured around country-specific reporting obligations, regulatory crimes tied to particular licensing regimes, and sanctions violations defined by one nation’s foreign policy all create potential double criminality failures.
Temporal Gaps
Norris demonstrated this clearly. If the conduct was legal in the requested state at the time it occurred, the requirement cannot be satisfied retroactively. A subsequent change in the law does not rescue an extradition request. The relevant date is when the conduct took place, not when the request was made.
Extraterritorial Overreach
El-Khouri addressed this directly. When a requesting state tries to claim jurisdiction over conduct that physically occurred elsewhere, the dual criminality test becomes harder to satisfy. The requested state’s courts must assess whether the physical acts, situated in their own territory, would constitute an offence. Attempting to stretch “effects” across borders to manufacture compliance is exactly what the Supreme Court pushed back against.
- The conduct is legal in the requested state (e.g., gambling, cannabis, certain financial activities)
- The charge relies on a uniquely domestic statute with no foreign equivalent (RICO, CCE)
- The conduct was legal at the time it occurred but later criminalised
- The requesting state claims jurisdiction based on “effects” rather than physical conduct
- The sentencing threshold (typically 12 months) is not met in both jurisdictions
- The request involves regulatory or administrative infractions that do not rise to criminal conduct elsewhere
Dual Criminality and the European Convention on Extradition 1957
The European Convention on Extradition, opened for signature in Paris on 13 December 1957, was the first major multilateral treaty to codify the dual criminality requirement. Article 2 of the Convention requires that the offence be punishable by at least one year of deprivation of liberty under the laws of both the requesting and requested parties.
More than 50 countries have ratified this Convention, making it one of the most widely adopted extradition instruments in the world. Its double criminality provision has served as the template for hundreds of bilateral treaties negotiated since.
The Convention also introduced flexibility. Article 2(2) permits contracting parties to limit extraditable offences through reservations, while Article 2(3) allows states to extend extradition to offences not covered by the treaty through executive discretion. These provisions give states room to negotiate, but the core requirement under Article 2(1) remains the bedrock.
Extradition shall be granted in respect of offences punishable under the laws of the requesting Party and of the requested Party by deprivation of liberty or under a detention order for a maximum period of at least one year or by a more severe penalty. Where a conviction and prison sentence have occurred in the territory of the requesting Party, the punishment awarded must have been for a period of at least four months.
Building a Dual Criminality Defense: Practical Strategy
A successful challenge on these grounds requires precision. You need to dissect the extradition request, identify the exact conduct alleged, and demonstrate that it falls short of criminal liability in the requested state. The process breaks down into five steps.
Step 1: Identify the specific conduct alleged. Strip the request back to its core. What did the person actually do? Ignore how the requesting state labels the offence. Focus on the physical acts described in the warrant or request. The El-Khouri decision confirmed that “conduct” means what it ordinarily means: the behaviour itself, not its downstream effects.
Step 2: Transpose the conduct into the requested state. Take that conduct and hypothetically place it in the jurisdiction where the person is located. Would it amount to a criminal offence there? This is the transposition exercise that UK courts perform under Sections 64 and 137 of the Extradition Act 2003. Be rigorous about this. Do not allow vague “equivalence” arguments to bridge genuine gaps in criminalisation.
Step 3: Check the sentencing threshold. Even if the conduct is technically criminal in both jurisdictions, the test also requires that it meets the minimum punishment threshold. Under most treaties and the Extradition Act 2003, the offence must carry a maximum sentence of at least 12 months’ imprisonment in both countries. Some treaties set the bar at one year, others at two. Check the specific treaty that governs the request.
Step 4: Research applicable exceptions. Is the request governed by a framework that exempts certain offences from the double criminality check? The EAW’s 32-category framework list is the most prominent example, but post-Brexit this no longer applies to UK proceedings. Other treaties may have their own carve-outs. Know the legal instrument before you plan your defense.
Step 5: Assemble expert evidence. These challenges often require expert evidence on foreign law. You may need a qualified lawyer from the requesting state to explain the precise elements of the charge, and a lawyer from the requested state to confirm that those elements do not map onto any local offence. This comparative legal analysis is the backbone of the defense.
Common Mistakes in Dual Criminality Challenges
I’ve seen this play out before. Solid double criminality arguments undermined by avoidable errors. These are the traps that catch people.
Confusing offence names with underlying conduct. The most common mistake. A person sees that the foreign charge has no equivalent statute in their country and assumes they are safe. But courts apply the conduct-based test. If the behaviour described, regardless of what it is called, amounts to a crime locally, the test is satisfied. You need to argue the conduct gap, not the naming gap.
Ignoring treaty-specific provisions. Every extradition treaty has its own double criminality clause. Some are broader than others. Some include offence lists that bypass the requirement. A generic argument that ignores the specific treaty language will fail. The starting point must always be the governing treaty or legal instrument.
Missing the temporal dimension. Was the conduct criminal at the time it occurred? Norris succeeded precisely because price-fixing was not a crime in the UK during the relevant period. If the law has changed since the alleged conduct, you may have a temporal argument on these grounds. Most practitioners overlook this angle.
Failing to challenge extraterritorial jurisdiction. After El-Khouri, this is a live issue. If the requesting state is asserting jurisdiction over conduct that physically occurred in a third country or in the requested state, the transposition exercise becomes more complex. Challenge the jurisdiction, not just the double criminality point, and the two arguments can reinforce each other.
Not instructing foreign law experts early enough. This is a comparative law exercise. Leaving expert evidence to the last minute gives the court less confidence in your position. The system is designed to move fast. Instruct experts the moment you identify a viable argument.
Dual Criminality Across Jurisdictions: Comparison Table
How strictly different countries enforce dual criminality varies significantly. This comparison covers the major extradition frameworks and their treatment of the principle.
| Jurisdiction | Governing Law | Test Applied | Minimum Sentence | Exceptions to Dual Criminality |
|---|---|---|---|---|
| United Kingdom | Extradition Act 2003, ss. 64, 137 | Conduct-based | 12 months | None post-Brexit (previously 32 EAW categories) |
| United States | 18 U.S.C. § 3184 + treaty | Conduct-based (Collins v Loisel) | 1 year (treaty-dependent) | Violent crimes against US nationals (no treaty required) |
| EU Member States (EAW) | Framework Decision 2002/584/JHA | Conduct-based with list exception | 12 months (3 years for list offences) | 32 framework list categories |
| Canada | Extradition Act, S.C. 1999, c. 18 | Conduct-based | 2 years | Limited (some treaty-specific) |
| Australia | Extradition Act 1988 | Conduct-based | 12 months | Limited (some treaty-specific) |
| European Convention States | European Convention 1957, Art. 2 | Conduct-based | 1 year | Reservations permitted under Art. 2(2) |
Understanding how your specific jurisdiction applies the test is not optional. It is the first question any extradition lawyer should answer. The Extradition Report provides jurisdiction-by-jurisdiction analysis of dual criminality standards across all major extradition frameworks.
Offences That Commonly Fail the Dual Criminality Test
Certain categories of offences consistently create double criminality problems. Not because the principle is ambiguous, but because criminal laws vary dramatically from one country to another.
Tax offences. Tax systems are uniquely domestic. A person cannot commit US tax fraud in a country that does not use the US tax code. Many extradition treaties historically excluded fiscal offences from the double criminality requirement altogether. While this has softened in recent years (the OECD pushed hard for tax offence extradition), genuine gaps remain where the underlying conduct does not constitute fraud or evasion under local law.
Securities and financial regulation offences. El-Khouri is the prime example. Insider trading laws, market manipulation statutes, and financial reporting requirements differ enormously between jurisdictions. What constitutes insider dealing under US securities law may not map onto the financial crime framework in the requested state.
Drug offences with legal divergence. Cannabis is the obvious case. A person charged with cannabis distribution in a jurisdiction where it is federally illegal cannot easily be extradited from a country where the same activity is lawful and regulated. As more jurisdictions legalise cannabis, this gap in the double criminality analysis will only widen.
Speech and expression offences. Blasphemy, sedition, lèse-majesté, and certain speech-related offences exist in some legal systems but not others. A country with robust free speech protections will not extradite someone for conduct that amounts to protected expression under its own constitutional framework.
RICO, CCE, and enterprise liability. As discussed above, these uniquely American constructs face inherent double criminality challenges. The argument that predicate offences satisfy the requirement has limits, particularly when the RICO charge itself is the only count carrying the requisite sentencing threshold.
Dual Criminality vs Other Extradition Defenses
The double criminality rule is one of several grounds on which extradition can be challenged. Understanding how it interacts with other defenses is critical for building a comprehensive strategy.
| Defense Ground | What It Challenges | Relationship to Dual Criminality |
|---|---|---|
| Dual criminality | Whether the conduct is criminal in both states | Core requirement; often the first analysis |
| Specialty principle | Prosecution for offences beyond those in the request | Complementary: even if dual criminality is met, the person can only be tried for the specified offences |
| Political offence exception | Whether the offence is political in character | Separate ground; can apply even when dual criminality is satisfied |
| Human rights (Article 3 ECHR) | Risk of torture or inhuman treatment | Independent; Soering v UK (1989) established this as a standalone bar |
| Passage of time / delay | Unreasonable delay making extradition unjust | Separate ground under s.82/s.87 EA 2003 |
| Forum bar | Whether the case should be tried domestically | May overlap when conduct occurred partly in the requested state |
| Proportionality | Whether extradition is proportionate to the offence | Can reinforce dual criminality arguments for minor offences |
A strong extradition defense rarely relies on a single ground. The double criminality argument is often the foundation, but layering it with human rights arguments, forum bar challenges, and proportionality objections creates a far more resilient position. Governments do not play fair in extradition proceedings. Your defense strategy should not be one-dimensional either.
Frequently Asked Questions About Dual Criminality
What is dual criminality in extradition?
Can dual criminality make extradition impossible?
Does dual criminality apply to European Arrest Warrants?
What is the difference between dual criminality and double criminality?
How does dual criminality work in UK-US extradition cases?
Can you be extradited for RICO charges under dual criminality?
What happens if the law changes after the alleged offence?
Is dual criminality required in every extradition case?
Does dual criminality require the offence names to match?
How did El-Khouri change dual criminality law in 2025?
Can dual criminality block extradition for tax offences?
What is the minimum sentence threshold for dual criminality?
Where can I get help with a dual criminality defense?
Final Thoughts on Dual Criminality
Dual criminality is not a technicality. It is one of the most fundamental protections in extradition law, and when it applies, it can stop a request dead in its tracks. The principle exists for a reason: no country should surrender a person to face prosecution for conduct that is perfectly legal under its own laws.
But the protection is not automatic. You have to raise it, argue it, and prove it. The conduct-based test gives requesting states room to manoeuvre, and governments will push the boundaries of what “equivalent” means. The El-Khouri decision pushed back. Norris pushed back. These cases exist because individuals and their lawyers did the hard comparative legal work and showed the court that the double criminality threshold was not met.
If you are facing an extradition request, the first question to answer is whether the conduct alleged actually amounts to a crime where you are. If it does not, that window closes fast for the requesting state. And if the answer is not clear-cut, that is where the real fight begins.
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Sources and References
- UK Parliament, Extradition Act 2003, Section 64
- Legal Information Institute, 18 U.S.C. § 3184: Fugitives from Foreign Country to United States
- Council of the European Union, Council Framework Decision 2002/584/JHA on the European Arrest Warrant
- UK Supreme Court, Norris v Government of the United States of America [2010] UKSC 9
- US Department of Justice, Criminal Resource Manual: International Extradition, 18 U.S.C. § 3184
- US Department of State, 7 FAM 1610: Extradition Introduction and Dual Criminality
- Office of Justice Programs, Problems of Double Criminality in CCE and RICO Extradition Cases
- Council of Europe, European Convention on Extradition 1957 (ETS No. 024)