In this post we differentiate between two types of retrospective rule making (RRM): RRM in the strong sense and RRM in the weak sense. We then argue that both types of RRM may violate the rule of law to a similar extent, and that both can be morally indefensible, and potentially illegal. We conclude by arguing that important aspects of UK immigration policy, namely the ever-increasing visa application fees and the introduction of an annual salary threshold, are the result of RRM in the weak sense, and that they are morally indefensible and perhaps also illegal. 

RRM in the Strong Sense, RRM in the Weak Sense, and Guiding People’s Behaviour

In the academic literature, RRM is often understood as a rule that changes the legal status or legal consequences of an act that was committed before the rule was created; or a rule that changes the legal status or legal consequences of a situation that existed (and ceased to exist) before the rule was created. This common perception is only partly accurate. There are in fact two types of RRM: RRM in the strong sense (the common perception as described above) and RRM in the weak sense.

RRM in the weak sense occurs when a rule changes the legal status or legal consequences of an act that has started before the rule was created, yet this is an ongoing act that is still being committed in the present and continues into the future; or when a rule changes the legal status or legal consequences of a situation that existed before the rule was created – and continues to exist after the rule was created.

An example of RRM in the weak sense would be a general legal norm that changes council tax rates, and applies that change from the moment that the legal norm is enacted (or at some point thereafter) – yet the change is applied to those who were already home owners or residents when that legal norm was enacted. Regardless of whether the retrospective application of the new rule is justified, it is still RRM, though in the weak sense. In this example, the RRM does not raise any moral or legal issues. In other cases, however, things can be more complicated.  

The main problem with RRM, in either sense, is that it fails to guide people’s behaviour, either completely or to a meaningful extent. It is that failure that requires clarifying the link between RRM and the rule of law. Here we subscribe to Joseph Raz’s perception of the rule of law that concludes, in short, that the purpose of the law is to guide people’s behaviour – and that the rule of law is a set of requirements that must be met in order for the law to be able to achieve the purpose of guiding people’s behaviour. By ‘guiding people’s behaviour’ Raz does not only refer to the ability to understand what the law says – and act accordingly. Rather, the law’s purpose to ‘guide people’s behaviour’ concerns people’s well-being and is meant to allow them to ‘find their way and to live well’.  

RRM in the strong sense always fails to guide people’s behaviour. RRM in the weak sense, however, fails to guide people’s behaviour only in cases where it is impossible, extremely difficult, or exceptionally costly to stop committing an act or to change a situation that started in the past and continues into the present and the future – and when those who are subject to the new rule wish to do exactly that – or when there is reliance in the sense that will be described below.

RRM: Moral Considerations

Classifying a legal norm as retrospective does not entail making a conclusive moral judgment about the retrospective application of the rule. Classifying a rule as retrospective is either morally neutral or no more than morally suspicious. The morality of RRM depends on other additional factors. RRM in the weak sense changes the rules of the game after the game has already started. But we need more than that in order to make a more serious claim about the morality (and possibly legality) of RRM. Four questions should be asked in order to evaluate the morality of RRM in the weak sense: (1) how severe the implications of the new rule are; (2) how difficult it is for those who are subject to the new rule to change an ongoing situation or ongoing status, or to stop committing an ongoing act; (3) would those who are subject to the new rule have changed their behaviour or decisions in the past, had they known that at some point in the future the new rule would be introduced; and (4) the public interest in the retrospective application of the rule.

Consideration 3 requires clarification. It is, in short, the question of reliance. But here we do not only ask whether those who were subject to the previous rule actually acted upon that rule or made their decision while relying on that rule. Rather, we ask a slightly different question: whether they would have acted in the same way if they knew that a new rule would be introduced in the future.

The example of the rules that govern non-EU immigration to the UK helps us to better understand RRM in the weak sense and its questionable morality and legality. More than a few aspects of said rules are examples of RRM in the weak sense. Here, we focus on only two aspects of the immigration policy regarding non-EU citizens: the annual salary threshold and the application fees.

UK Immigration Policy Regarding non-EU Citizens: Moral Considerations

The first example concerns the annual salary threshold. Those who entered the UK in 2011 under a Tier 2 visa could apply for residency after living in the UK for 5 years. In April 2012, the rules changed and required applicants for settlement to have a Tier 2 visa for at least 5 years and to meet a minimum annual salary threshold of £35,000 (which was more than the median salary in the UK at the time of £28,028). Accordingly, those who entered the UK in 2011, under a reasonable assumption that eventually they would have Indefinite Leave to Remain (ILR), had to leave the UK by 2016 if the main applicant did not earn more than £35,000 per year. From 1 December 2020, the system was updated again, retrospectively (in the weak sense), and Tier 2 visas were replaced by a general Skilled Worker Visa. There is now a minimum annual salary threshold of £41,700 per year.

This is RRM in the weak sense as it changes the legal implications of an ongoing act or situation that started in the past and continues into the future, i.e. living in the UK as a non-citizen. The new rules, therefore, failed in guiding the behaviour of those who entered the UK before these rules were enacted.

This RRM gives its subjects a choice: earn £35,000 a year – or leave the UK. This is not a real choice. People have a real choice when they have an adequate number of valuable options to choose from. A decision to leave one’s country, home, and previous life, and emigrate to another country, with an intention to stay there permanently, normally entails significant costs and irreversible and life-changing sacrifices. In the example above, this RRM fails in guiding people’s behaviour, and prevents them from making rational and well-informed long-term plans. In Raz’s terminology, it adversely affects people’s well-being and doesn’t allow them to ‘find their way and to live well’. Since the results of this RRM may be severe, and since it is extremely difficult to stop the relevant ongoing act or situation, it is potentially immoral.

To further evaluate the morality of this RRM in the weak sense, we must ask whether those migrants who now live and work in the UK would not have migrated if they knew, before migrating, about the future changes to the rules. If the answer is yes – we have strong reliance on the previous rules and presumed immorality. In such a case, the RRM in the weak sense can be justified only where compelling reasons outweigh the legitimate interests of those who are affected by it. If the answer is no – there is no reliance, but as we shall see below, that alone does not make the RRM morally justified. Given the presumption of immorality, those who introduced the above rules and decided to apply them retrospectively must refute said presumption. This can be done by applying the proportionality test; applied here as a moral, rather than legal, test.

Firstly, we consider the possible justification for introducing a salary threshold of £35,000 a year for non-EU migrants. The reasoning for the change was to cut the number of such migrants and their dependants granted permanent residency each year from 60,000 to 20,000. We will assume that this is a legitimate aim. As to the suitability test, increasing the salary threshold is likely to achieve its aim, at least in part. Regarding the necessity test, we assume that there are no equally effective but less intrusive measures (even though there may be). We are left with whether the objective to reduce the number of immigrant residents is a sufficiently important justification for the violation of the rule of law, and for harming people’s important and legitimate interests.

We argue, without elaborating on this point, that the RRM in this case is disproportionate. The retrospective change prevented those who already moved to the UK from making an informed decision as to whether to immigrate to the UK. Those who moved to the UK with no prospects of earning more than £35,000 a year would probably not have made this life-changing decision had they known that this new restriction would be introduced in the future. These people cannot merely decide to earn £35,000 a year. The severity of the harm caused to thousands of people, and the gross violation of the rule of law in this case cannot be justified by the wish to cut the number of non-Europeans granted residency each year.

A second example is the changes made to the ILR application fees for non-EU migrants. From 2014 onwards, the fees were frequently increased. For example, they increased from £1,093 in 2014 to £1,500 in 2015, then to £1,875 in 2016, and again to £2,297 in April 2017 and £2,389 in 2018. The application fee then froze until 2022, largely due to the Covid-19 pandemic. The fees as of April 2026 are £3,226 for main applicants and their dependants (regardless of their age). Around this timeline, the Immigration Health Surcharge (IHS) was also introduced – and kept increasing. The IHS is a fee that migrants in the UK are required to pay in order to have access to the NHS. Access to the NHS is free to all UK citizens. Migrants are required to pay the IHS even when they pay their national insurance contribution like all other UK citizens. The IHS was introduced in April 2015 at £200 per year. In December 2018 it increased to £400 per year. In October 2020 – to £624 per year, and as of 6 February 2024 it is £1,035 per year.

These changes were applied to those already living and working in the UK, which makes them RRM in the weak sense. A proper, fairer way of applying changes to application fees and the IHS, especially when the changes are meaningful, would be to apply them to those who enter the UK only after the change has been made, i.e. prospective rulemaking that complies with the rationale of the rule of law.

Even though the changes to the application fees were always RRM in the weak sense, it is likely that in most cases, there was no reliance. It is likely that most immigrants would have still come to the UK even if they knew that their application fees will significantly rise in the future. Yet, even when there is no reliance, the retrospective application of the increases of both application fees and IHS clearly takes advantage of the vulnerable position of many migrants, who, after already making the life-changing and costly decision to leave their home countries and come to the UK, will not easily leave the UK even in the face of policies that exploit them financially. The immorality of the RRM in the weak sense in this case, still, therefore, very much exists, even with lack of reliance.

UK Immigration Policy Regarding non-EU Citizens: Legal Considerations

The “governing norm” of all immigration rules, which was created by government, rather than Parliament, states that ‘the Immigration Rules are subject to change and applicants must see the requirements in place at the time they make their application to settle’. Put differently, the government reserves the right to apply its immigration rules retrospectively. That gives rise to a ‘jurisprudential’ problem – and a legal-doctrinal one, with the former informing the latter.

From a jurisprudential perspective, even if the rule of law is not entrenched in a written, legally supreme Constitution, government is still bound by “the law”, i.e. by primary legislation. Government, which is created by the law and is subject to the law, cannot assume the authority to frustrate the very purpose of the law, which is to guide people’s behaviour. It cannot undermine the purpose of the very “thing” that creates it and gives it its powers. It therefore cannot assume the authority to violate the rule of law (the purpose of which is to allow the law to guide people’s behaviour) unless explicitly authorised to do so by Parliament. It cannot assume the authority to create retrospective rules if it results in a complete failure to guide people’s behaviour (subject to exceptional circumstances). To be clear: violations of the rule of law can be morally justified. Our point here is that RRM, also in the weak sense, requires justification, either by applying the proportionality test or by other means, yet it seems that there has never been an attempt to justify the RRM here, presumably also because it was never perceived as such. 

From a more legal-doctrinal perspective, section 1(a) of The Constitutional Reform Act 2005 entrenches ‘the constitutional principle of the rule of law’. If the UK does have an unwritten constitution, the rule of law was always part of it. Since 2005, however, the rule of law is a “statutory constitutional principle”. If parliamentary sovereignty and the rule of law are two of the cornerstones of the UK constitution, and if the rule of law is a statutory constitutional principle, then it must mean that government has no legal power to create general legal norms that contradict the rule of law, unless specifically authorised to do so by Parliament – or if it is found that the RRM, including in the weak sense, is legally reasonable or proportionate. Thus, and in our case, if the rule of law prohibits RRM (including RRM in the weak sense), then government has no legal power to authorise itself to apply general legal norms retrospectively. Section 3(2) to the Immigration Act authorises the Secretary of State to lay before Parliament statements of the immigration rules – and changes in the rules. Nothing in this section or anywhere in the Immigration Act implies that the Secretary of State is authorised to apply new rules retrospectively. This means that the “governing norm” of all immigration rules has no legal effect. It is plainly ultra vires. The retrospective application of immigration rules (also in the weak sense) can only be legally valid if Parliament specifically authorised government to do so – and it did not – or if the retrospective application is proportionate or reasonable – yet it is not. A different question is whether claims regarding said illegality are likely to succeed in court. In short, even though the legal argument here does have some support in the case law that accords appropriate weight to the constitutional principle of the rule of law, we suspect that considerations of justiciability and deference may result in judicial reluctance to allow said legal argument. That, of course, takes nothing from the strength of the argument. All it means is that for reasons pertaining to judicial policy, government is likely to be allowed to continue acting illegally regarding immigration rules.        

Conclusion

The introduction of the annual salary threshold and the constant significant rise in ILR application fees made migrants already living in the UK significantly worse-off. These retrospective changes (in the weak sense) applied to those who already lived and worked in the UK – treating them as “captive subjects”, denying their autonomy or giving them a “choice” between bad options and even worse ones. These changes were in gross violation of the rule of law, at least in cases where they completely failed to guide people’s behaviour. The legality of this RRM is doubtful. Its immoral nature is indisputable.

Yossi Nehushtan is Professor of Law and Philosophy, Keele University. Faye Thomas is a graduate of Keele University (LLB) and Cambridge University (LLM). Our thanks are due to Paul Scott and Leah Trublood for their extremely helpful comments and suggestions. 

This post summarises a few points that are discussed in full in: Yossi Nehushtan and Faye Thomas ‘Two Types of Retrospective Rule Making, the Rule of Law, and UK Immigration Policy’ {forthcoming, 34 The Denning Law Journal (2026)}.

(Suggested citation: Y. Nehushtan and F. Thomas, ‘Retrospective Rule Making, the Rule of Law, and UK Immigration Policy’, U.K. Const. L. Blog (27th May 2026) (available at https://ukconstitutionallaw.org/))