Legislating for the past: What is retrospective legislation and when is it ok?

Two huge donations to Reform UK have prompted a debate about whether the government should introduce retrospective legislation to outlaw or reverse them.

Retrospective legislation can be defined as legislation which in some way has legal effects on actions or events occurring before it comes into force. Examples might be legislation criminalising (or de-criminalising) past conduct; validating administrative acts which were unlawful at the time they were carried out; or reversing the effect of a court judgment – particularly if a judgment is considered to be a “surprise” and lots of people have honestly ordered their affairs on a view of the law which the court has now ruled to be wrong. Specific examples are discussed in this House of Commons Library briefing from 2013. ¹⁹ https://researchbriefings.files.parliament.uk/documents/SN06454/SN06454.pdf

There is no absolute rule against retrospective legislation

The reasons against retrospective legislation are generally considered to be that it is unfair for citizens and businesses to be judged against laws which did not apply (and which they obviously could not know about) at the relevant time, and that it tends to undermine legal certainty and confidence in the law.

However, as the House of Commons Library note illustrates, there has never been an absolute rule against retrospective legislation. Constitutionally, parliament can enact any laws it chooses, including retrospective ones. In law, the courts apply a presumption that parliament does not legislate retrospectively without clear words, so if a statute is to apply to past conduct or events it should say so expressly. In practice, successive governments have resorted to retrospective legislation only in exceptional circumstances and where there is considered to be a strong public interest in doing to.

The Cabinet Office Guide to Making Legislation ²⁰ https://assets.publishing.service.gov.uk/media/68c14f2b7596dbfa052bfde2/2025_Guide_to_Making_Legislation_-_September.pdf  says: “Any proposal for a provision to have retrospective effect, to be formally retrospective or to commence earlier than two months after Royal Assent must be agreed by the Law Officers”, i.e. the attorney general, solicitor general and advocate general for Scotland. The approach of the current law officers – which is consistent with that of previous administrations – was set out recently in this parliamentary answer ²¹ https://questions-statements.parliament.uk/written-questions/detail/2026-08-28/20417  from the solicitor general: they will consent to retrospective legislation only where “the general public interest in the law not being changed retrospectively is outweighed by the public interest of legislating retrospectively in that case”. In other words, it all comes down to an assessment of the public interest.

Relevant public interest factors might include the gravity of the “mischief” or harm which the legislation is designed to cure, the period of time covered by it, the number and nature of the persons to whom it applies, the availability of protections to address hardship in particular cases, and the fact that the relevant changes to the law were announced in advance, so that people had at least some opportunity to prepare for them.

There are different types of retrospectivity

There are different types and degrees of retrospectivity. At one extreme, legislation to create retrospective criminal offences – where I might be prosecuted and punished for acts which were lawful at the time I did them – will almost always be regarded as unfair and unacceptable. It is also likely to breach Article 7 of the European Convention on Human Rights (ECHR). ²² https://questions-statements.parliament.uk/written-questions/detail/2026-08-28/20417

On the other hand, legislation to de-criminalise past conduct or quash past convictions might well be considered justified in the public interest, where there has been obvious injustice, or where societal attitudes to the relevant conduct have changed in the meantime. One example is the Post Office (Horizon Systems) Act 2024, which retrospectively quashed wrongful convictions of postmasters and others affected by the operation of the flawed Horizon software system. Another example is the so-called “Alan Turing” law in the Policing and Crime Act 2017, conferring posthumous pardons for offences committed under old laws prohibiting homosexual activities.

Outside the criminal law, legislation to validate past administrative action might be acceptable if everyone (or most people) had previously proceeded on the (mistaken but reasonable) belief that the action was lawful anyway, and failure to correct the position retrospectively might cause more disruption and unfairness than doing so. An example of that is the Police (Detention and Bail) Act 2011. This reversed a court decision on the calculation of the detention timetable under PACE, “in view of the serious impact of the judgment on the police’s ability to investigate crime and protect the public” (to quote from the government’s explanatory notes on the bill).

One particular category of retrospective legislation is that dealing with taxation. This House of Commons Library briefing  ²³ https://researchbriefings.files.parliament.uk/documents/SN04369/SN04369.pdf  discusses the arguments for and against such legislation, including the wish of successive governments to tackle particular tax avoidance schemes, which though lawful at the time were deemed to be pernicious in public policy terms. Specifically, it gives examples of changes to tax law being back-dated to the day of the change being announced (or even earlier), in order to prevent “forestalling activity” or distortion to market behaviour in the meantime.

Legislation can affect existing rights without being retrospective

The mere fact that legislation affects pre-existing affairs does not of itself make it retrospective. All legislation is designed to change something: no-one is entitled to assume that their lives, businesses or assets will never be affected by future changes in the law. For instance, legislation which affects for the future the use or value of pre-existing assets and rights (including contractual rights), or even provides for the compulsory confiscation of such assets – for example a ban on the possession or sale of objects previously permitted but now deemed to be dangerous – will not necessarily be technically retrospective.

Such legislation might prompt a challenge under Article 1 of Protocol 1 to the ECHR, which provides for the protection of property rights. But that article permits deprivation of possessions “in the public interest and subject to the conditions provided by law” (the availability of compensation might be relevant to the public interest assessment). It is also stated not to “in any way impair 
the right of a State to enforce such laws as it deems necessary to control the use of property in accordance with the general interest or to secure the payment of taxes or other contributions or penalties”.

The Representation of the People Bill could result in legal consequences for (past) donations

The lawfulness of donations to political parties is governed by the Political Parties, Elections and Referendums Act 2000. The Representation of the People Bill, which is currently going through parliament, amends the rules on such donations (among other things). A number of provisions of the bill are already retrospective, in the sense that they are back-dated to 25 March 2026 – the date on which the government announced the intended policy. Those provisions include a ban on donations in the form of cryptoassets, and a power for the secretary of state to make regulations about donations from overseas donors. The government has said it intends to use that power to impose a £100,000 annual cap – running from 25 March 2026 – on donations from British voters living abroad; and to apply that cap to any overseas elector returning to the United Kingdom until he or she has been resident here for a full calendar year – a rule which would again apply retrospectively from 25 March 2026.

Justifying these provisions, the government’s minister in the Lords said: “We will not allow bad actors to funnel money into our elections in advance of a change in the law. There is a clear time-critical risk of evasion of these new rules that would undermine their purpose if they were brought in at a later date.”

The government is said to be contemplating amendments to the bill to make further retrospective provision catching the two big donations to Reform UK. Such amendments might include further back-dated residency requirements. It is possible to imagine broader changes, for example a cap on the total of all donations made to a party over a period beginning on (say) 25 March 2026 or some other date in the past. Such provisions would not necessarily render donations unlawful at the time they were made, and need not create any retrospective criminal offence ²⁴ The Bill creates criminal offences relating to the failure to return unlawful donations, but even where such a donation was made before commencement, the offences relate only to failure to return the money in a specified period after commencement. Thus the government considers those provisions to be prospective only and compatible with the ECHR: see the government’s ECHR memorandum. https://bills.parliament.uk/publications/67601/documents/8722 , but would undoubtedly have legal consequences for past conduct. We will see what happens as the bill continues its passage.