This guide is maintained as a current resource for September 2026 and covers only the laws of England and Wales. Information is for general guidance, not legal advice. Consult a qualified solicitor for advice specific to your situation.
Explore when a contract becomes void for illegality in England and Wales. This comprehensive guide explains statutory and common law illegality, public policy considerations, legal consequences, leading case law, and practical steps to avoid void contracts in business agreements.
Contracts are foundational to business dealings, setting out the rights and obligations of parties entering into commercial relationships. However, even where the key elements of a contract - offer, acceptance, and consideration - appear present, a contract may still be void for illegality if it contravenes statute, public policy, or common law principles. In England and Wales, the law treats illegal contracts as unenforceable to protect the integrity of the legal system and serve the public interest. This article explains when a contract is void for illegality, the legal principles involved, leading cases, practical consequences, and steps parties can take to avoid unintended unenforceability.
Understanding Illegality in Contract Law
A contract is said to be illegal when its formation, purpose, or performance involves conduct that is prohibited by law or contrary to public policy. An illegal contract is generally void ab initio - meaning it is treated as if it never existed and cannot be enforced by any party in the courts or tribunals of England and Wales. This reflects the legal maxim ex turpi causa non oritur actio (“no action arises from a dishonourable cause”), which prevents courts from assisting parties whose cause of action is founded on wrongful conduct.
Illegality can arise under statute - where legislation expressly or impliedly prohibits a type of contract - or under common law - where agreements are deemed contrary to public policy, even if not expressly outlawed by statute.
Contracts Illegal at Formation
Some contracts are illegal from the outset because they require the parties to perform unlawful acts or because their performance necessarily entails breaking the law. If a contract cannot be performed without committing an illegal act, it is void and unenforceable.
Examples include:
- Agreements to commit a crime or tort: Contracts to engage in criminal conduct (for example, conspiracies to defraud or drug trafficking) are illegal and unenforceable.
- Statutory prohibitions: Where a statute prohibits certain contracts or requires licences or permissions that are not obtained, the contract can be illegal. For instance, contracts involving sales or transfers of goods or services that are themselves prohibited by law will be void.
- Violation of regulatory regimes: Contracts that breach financial regulation, insider trading laws, or anti‑corruption statutes may be held void for illegality because their performance would contravene specific legal prohibitions.
In Foster v Driscoll, the Court of Appeal held that a partnership agreement to supply whisky in breach of United States prohibition laws was unenforceable - even though the arrangements were not unlawful in England - because the contract's purpose was to break the law.
Common Law Illegality and Public Policy
In addition to statutory illegality, English law recognises contracts as illegal at common law when they conflict with fundamental principles of public policy. These are not necessarily criminal, but they are considered harmful to society if enforced.
Common law illegality categories include:
- Contracts to defraud public revenue or corrupt public officials.
- Contracts that restrict fundamental freedoms (for example, agreements to oust the jurisdiction of courts).
- Contracts that promote immoral or harmful activities, such as agreements harmful to family relations or societal order.
The policy behind these rules is that courts should not enforce agreements that undermine the legal or moral framework of society.
Contract Illegal by Performance
A contract that was lawful when formed can also become illegal if its performance involves illegal conduct. If a contract's execution results in unlawful acts, a court may refuse to enforce those aspects that are illegal, though the contract itself might remain valid if the illegal element is incidental and severable.
For example, delivering goods in breach of a statutory requirement could affect the legal rights of the parties if the breach goes to the substance of the agreement, but minor or incidental illegal acts in performance (such as inadvertent traffic offences) generally do not void the contract itself.
Severability of Illegal Terms
A contract may contain both lawful and unlawful provisions. In such cases, the courts may apply the blue pencil doctrine or statutory severability principles to remove illegal terms while retaining enforceable ones, provided the contract can stand independently after the illegal provisions are severed.
This approach allows commercial agreements to remain enforceable where the unlawful aspects do not go to the core of the contract.
Legal Consequences of Illegality
If a contract is adjudged illegal and therefore void:
- It cannot be enforced in court, meaning no party can sue for performance or damages under that contract.
- No rights arise from an illegal contract, and neither party can rely on the courts to uphold obligations that stem from it.
- Restitution may be limited. The courts have some flexibility in equitable remedies like restitution - returning benefits conferred - particularly following Patel v Mirza. In that case, the Supreme Court held that recovery of money paid under an illegal contract may be permitted where it serves the public interest and avoids unjust enrichment, even if the contract itself was illegal.
The extent to which restitution is available depends on the seriousness of the illegality, whether one party was innocent, and whether allowing recovery would harm public policy interests.
Case Law Illustrating Illegality
Holman v Johnson (1775) remains a foundational case, articulating the principle that courts will not assist a party whose action arises from illegal or immoral conduct. However, in that case the contract was enforced because the seller had not engaged in unlawful conduct; he simply sold tea knowing it would be smuggled, which was insufficient to deny enforcement because he did no illegal act himself.
Patel v Mirza (2016) updated the approach to restitution and illegal contracts, emphasising that courts should assess whether denial of a claim on the basis of illegality would harm broader public policy, considering the purpose and proportionality of enforcement.
Practical Considerations for Businesses
Identifying Illegal Contracts
Businesses should ensure that contracts do not require or involve:
- Acts that are expressly prohibited by statute, such as illegal supply or trading arrangements.
- Common law illegal purposes, such as agreements contrary to public policy.
- Terms that may become illegal due to changing laws or regulatory frameworks.
Legal review of contracts can prevent unintended drafting of illegal or unenforceable provisions.
Managing Illegal Contract Risks
- Include severability clauses to allow lawful parts of a contract to remain enforceable if other provisions are illegal.
- Seek specialist advice where contracts touch on regulated sectors (finance, competition law, public procurement).
- Monitor statutory changes, as evolving legal regimes may turn previously lawful contracts into illegal ones requiring adjustment or avoidance.
Key Takeaways
A contract in England and Wales may be void for illegality when its formation, performance, or purpose involves unlawful activities or contravenes public policy. Illegal contracts are generally treated as if they never existed and cannot be enforced in courts or tribunals. Illegality can arise under statutes, common law prohibitions, or when performance would require illegal acts. A contract with illegal terms may sometimes be partially enforceable if the unlawful elements can be severed. Key cases such as Holman v Johnson and Patel v Mirza illustrate how courts balance enforcement with public policy and justice considerations. Businesses should identify and avoid illegal contract terms and seek timely legal advice to protect their commercial interests.
