A fundamental principle of the British constitution is that of parliamentary sovereignty, which A.V. Dicey defined as “the right to make or unmake any law whatever … no person or body is recognised by law of England as having a right to override or set aside the legislation of Parliament”. This means that traditionally, courts become subordinate to Parliament, simply enforcing the legislations that Parliament passes. However, over the past few decades, the courts have gradually had more confidence and ability to act in ways similar to that of constitutional courts in nations such as the United States and Australia, though it is still clear that Parliament holds the most power. The greater confidence and ability courts now hold was most notably symbolised by the Constitutional Reform Act 2005 (CRA 2005), which although by itself did not grant new powers to the judiciary, did signify their increasing ability to keep Parliament under ever closer scrutiny.A result of parliamentary sovereignty is that it distorts another fundamental principle found in most, if not all, Western democracies – that of the separation of powers. The separation of powers is the idea that public power is distributed between a legislature (that represents the people and makes legislations), a judiciary (that interprets the law and deals with legal disputes) and an executive (that makes and implements public policies). Furthermore, the three branches should be kept independent to ensure that no branch attains excessive power, allowing each branch to maintain checks and balances on the others. In the UK, this separation is very blurred as the Cabinet (executive) is drawn from Parliament (legislature). Further, parliamentary sovereignty restricts the judiciary’s ability to maintain strong checks and balances on the legislature, and by extension the executive. This imbalance distinguishes the UK from nations such as the United States, where their constitution sets out clear lines separating the three branches – the President (executive) may veto any bill passed by Congress (legislature), but Congress can then override the veto with a two-thirds majority, thus allowing each branch to maintain clear checks and balances on the other. Further, as a result of Marbury v Madison, the US Supreme Court also has the power of judicial review to declare any legislation passed by Congress as unconstitutional and therefore invalid, thus giving the judiciary a clear method to maintain checks on Congress. Meanwhile Australia, another common law jurisdiction, continues to follow the British model of parliament, therefore there is also no clear distinction between the legislature and executive. However, there is a major difference between the Australian and British judiciaries: Australia, having adopted the US model for its judiciary, has a highly independent and much more powerful judiciary, with broad capabilities to exercise judicial review similar to the US, most famously demonstrated in Australian Communist Party v Commonwealth, where the High Court ruled that the Communist Party Dissolution Act 1950 was invalid and beyond the powers granted to Parliament.In the UK, courts do not have such a broad ability to strike out legislation that they deem as unconstitutional. Being subordinate to Parliament, courts are restricted to only being able to exercise judicial review on secondary legislation. This is mainly due to parliamentary sovereignty, but it can be argued that there has always been practical restrictions on the absoluteness of the principle, long before the passage of the CRA 2005, and courts have been willing to use these limitations to enhance their role in maintaining checks against Parliament. The main internationally imposed restriction on parliamentary sovereignty arose from the passage of the European Communities Act 1972, which resulted in ‘EU law now enjoying de facto supremacy in the UK’. This was mainly due to the principle of EU supremacy developed in Costa v ENEL, later reaffirmed in UK domestic law by cases such as Factortame, with Lord Bridge stating that it had ‘always been clear that it was the duty of a United Kingdom court … to override any rule of national law found to be in conflict with any directly enforceable rule of Community law’. Further entrenchment of European law into domestic law came with the passage of the Human Rights Act 1998 (HRA 1998), which gave courts a new method of keeping check on Parliament under s.4 of the HRA 1998. Section 4 allowed the courts to declare that any legislation was “incompatible” with any of the rights set out in the European Convention of Human Rights. This ability still did not give courts the power to strike out such pieces of legislation, as the Act also explicitly states that ‘a declaration made under this section – does not affect the validity … and is not binding on the parties’. Nevertheless, it allows the courts to apply political pressure on Parliament, potentially creating political backlash by the electorate and ‘triggering the possibility of fast-track amendment’ by Parliament in order to not be seen as violating human rights. However, the non-binding nature of the declaration of incompatibility, and the still-prevailing dominance of parliamentary sovereignty have resulted in cases like Hirst v UK (No. 2), where Parliament ultimately asserted its sovereignty and decided to ignore the European Court of Human Rights’ decision that a blanket ban on prisoners’ right to vote was contrary to the ECHR, with the BBC reporting that then-PM David Cameron said ‘no one should be under any doubt – prisoners are not getting the vote under this government’. It can be argued that the passage of legislations such as the ECA 1972 and the HRA 1998 were essentially self-imposed restrictions by Parliament on its own sovereignty, and that Parliament effectively gave courts the ability to challenge executive decisions on the grounds of human rights found in the ECHR. Given that the strength behind all human rights claims for judicial review originate from the ECHR there is the possibility that following Brexit, much of the justifications behind such judicial review claims would not be transferred to the post-Brexit legal situation. Currently, this would depend heavily on how s 4(1) of the European Union (Withdrawal) Bill 2017-19, which states that ‘any rights, powers, liabilities, obligations, restrictions remedies and procedures’ arising from s 2(1) of the European Communities Act 1972 will continue to be recognised and enforceable under domestic law. The main issue is whether this extends to the ECHR, and furthermore whether it would allow for altering the HRA 1998’s basis in the ECHR to the domestic equivalent post-Brexit. This cannot be answered right now, especially since as of 24 Jan 2018, the Bill has only finished its first reading, thus can still be subject to drastic changes. Outside of using international conventions and laws, UK courts have also been slowly building confidence to increasingly scrutinise government domestically through various cases. As Jeffrey Jowell notes, ‘it used to be that the courts would not readily scrutinise the exercise of official discretion outside of the loose Wednesbury formula’, alluding to the fact that in the 1950s the courts generally showed deference to administrative decisions and would only intervene if the decision was so unreasonable and matched the Wednesbury test. However, over the past few decades, the courts have increasingly become more willing to scrutinise decisions and secondary legislations over ever-widening reasonings. The first notable case in recent history that marked the growth of judicial review was Ridge v Baldwin, which KJ Keith described as ‘one of the landmarks in the development of administrative law’, and gave courts the ability to apply principles of “natural justice”, such as the right to a fair hearing, to the decisions made by government. This was then followed by cases such as Padfield, which allowed courts to scrutinise the discretionary powers of government ministers, and Anisminic, which showed, amongst other things, the court’s reluctance to accept “ouster clauses” that attempt to ensure decisions and secondary legislations ‘shall not be called into question in any court of law’. Finally, the GCHQ case took the courts role one step beyond parliamentary decisions, holding that where an individual’s ‘private rights or legitimate expectations’ were affected by the Royal prerogative, it too can be subjected to judicial review. The culmination of the growing sentiment within the judiciary that the courts potentially should play a greater role similar to courts in the US and Australia came from the various obiter delivered in Jackson, such as Lord Hope’s remark that: ‘Parliamentary sovereignty is no longer, if it ever was, absolute … The fact that your Lordships have been willing to hear this appeal and to give judgment upon it is another indication that the courts have a part to play in defining the limits of Parliament’s legislative sovereignty’. Although this comment, and similar remarks by Lord Steyn and Lady Hale have no binding value, it presents the clearest sign yet that some of the top figures in the judiciary have recognised the growing importance of the judiciary in holding Parliament accountable. Furthermore, since these cases are all decided based on domestic principles, the potential issue raised in the earlier paragraph regarding the status of the ECHR post-Brexit would not apply, and so domestic precedent would allow judicial review to maintain most of the development it has seen over the past few decades. Parliament itself seems to have recognised the judiciary becoming more independent, confident and able to challenge decisions made by ministers and other public bodies. This recognition can be seen to be reflected by the CRA 2005, which although may not have increased the abilities of the courts or gave statutory authority to the developments in judicial review made over the past few decades, did made various procedural elements less political in its execution. This gives the judiciary at least a nominal sense of independence, in line with the idea of separation of powers, but without enhancing the judiciary’s ability to in fact maintain strong checks and balances and act similar to constitutional courts in places such as the US and Australia. This can be seen through the fact that even though the Supreme Court is a completely separate entity in name from the original House of Lords appellate committee, the same Law Lords that sat in the House of Lords appellate committee became Lord Justices of the Supreme Court. Another example of greater political independence can be seen through the changing of the appointments system from the Queen appointing judges on the advice of the Lord Chancellor to the creation of an independent Judicial Appointments Commission under s 61 of the CRA 2005. Even though no part of the Act gives the judiciary new powers, it serves as an important sign that the judiciary has increasingly become more independent and less subordinate to Parliament.It is clear that despite the theoretical fundamentality of the principle of parliamentary sovereignty to the British constitution, in reality it has been subjected to various limitations, both self-imposed by Parliament through legislation and by the judiciary through case law. Such limitations to parliamentary sovereignty has allowed the judiciary to grow more confident in its ability to exert pressure and maintain checks on Parliament. Even though the court’s ability to maintain checks and balances on the other branches of government the courts in the UK are still not as powerful as courts in nations such as the US and Australia, there has been a steady expansion of the capabilities exercised by the courts, culminating in the independence of the judiciary shown by the CRA 2005. The Act, at least nominally, marked the independence of the UK judiciary and its growing powers as a separate Supreme Court, as opposed to being an appellate committee within the upper house of the UK parliament. All of these points have resulted in parliamentary sovereignty clearly no longer being absolute, and should the obiter in cases like Jackson be followed in the future, British courts would be able to act further in line with nations like the US and Australia, maintaining even stronger checks and balances on government.