Separation between the Legislature and the Judiciary
The relationship between Parliament (the legislature) and the courts (the judiciary) in the United Kingdom's constitutional order is governed by a combination of statutory provisions, constitutional conventions, and common law doctrine. Whilst the principle of separation of powers demands that the two institutions remain functionally and institutionally distinct, the history of the British constitution reveals periods of significant overlap. This article examines the formal mechanisms of separation, the historical overlaps that once existed, the reforms introduced by the Constitutional Reform Act 2005, and the system of checks and balances that currently operates between Parliament and the courts.
Statutory Separation: The House of Commons (Disqualification) Act 1975
The most direct statutory mechanism separating the judiciary from the legislature is s 1 House of Commons (Disqualification) Act 1975, which disqualifies holders of judicial office from membership of the House of Commons. This provision ensures that those exercising the judicial function of interpreting and applying the law cannot simultaneously sit as elected legislators. The rationale is straightforward: a judge who is also a Member of Parliament would be placed in the constitutionally untenable position of adjudicating upon statutes in which he or she had participated as a legislator.
Constitutional Conventions: The Sub-Judice Rule and Mutual Restraint
Beyond statute, the separation of the legislature and the judiciary is reinforced by a set of constitutional conventions. The most significant is the sub-judice rule, under which Parliament refrains from debating the details of cases that are either currently before the courts or are about to come before them. This convention protects the integrity of judicial proceedings from political interference and preserves the autonomy of the judicial decision-making process.
Equally important is the convention of mutual restraint in public commentary. By convention, Members of Parliament do not criticise individual judges, and members of the judiciary do not involve themselves in partisan political activity. These conventions operate to maintain the appearance and reality of judicial independence — a cornerstone of the rule of law — and to prevent the judiciary from being drawn into political controversy in a manner that might compromise public confidence in its impartiality.
Parliamentary Privilege: Article 9 of the Bill of Rights 1689
A further dimension of the separation is provided by Article 9 Bill of Rights 1689, which establishes the freedom of speech and debate within Parliament. Under this provision, proceedings in Parliament cannot be impeached or questioned in any court or place outside Parliament. In practical terms, this means that courts cannot impose legal liability upon a Member of Parliament for anything said in the course of parliamentary proceedings. The effect is to create a constitutionally protected space — the floor of Parliament — into which the judiciary cannot reach. This reciprocal arrangement reinforces the boundary between the two institutions: just as Parliament does not intervene in pending judicial proceedings, so too are the courts excluded from scrutinising what is said within Parliament.
Overlap and Its Problems
Two Historical Overlaps: The Appellate Committee and the Lord Chancellor
Despite the formal mechanisms of separation described above, the British constitution historically exhibited two significant areas of overlap between the legislature and the judiciary.
First, the Appellate Committee of the House of Lords — the highest court of appeal in the United Kingdom for most purposes — was formally a committee of the upper chamber of the legislature. The Law Lords who sat on that committee were members of the House of Lords and were therefore simultaneously part of the judiciary and part of Parliament. Although by convention they refrained from speaking in legislative debates on politically contentious matters, the structural overlap remained constitutionally troubling.
Second, the Lord Chancellor occupied a uniquely problematic tripartite position. He was the Speaker of the House of Lords (the presiding officer of the upper chamber of the legislature), a Cabinet minister (and therefore a member of the executive), and the head of the judiciary. This concentration of functions in a single office represented a direct contradiction of the principle of separation of powers and drew sustained criticism from constitutional scholars and human rights organisations alike.
The Constitutional Reform Act 2005
The Constitutional Reform Act 2005 addressed both of these structural deficiencies. It established a new, independent Supreme Court of the United Kingdom, formally separating the apex of the judicial hierarchy from the House of Lords. The Justices of the Supreme Court sit in their own building and no longer hold seats in the legislature. The Act also transferred the Lord Chancellor's role as head of the judiciary to the Lord Chief Justice, thereby removing the most egregious instance of an individual simultaneously holding legislative, executive, and judicial functions. These reforms represented the most significant structural change to the relationship between the judiciary and the legislature in the modern era.
The Judiciary's Legislative Functions: Three Theories
The separation of the legislature and the judiciary is complicated further by the recognition that courts inevitably perform functions that bear a resemblance to law-making. Three principal theories have been advanced to explain the nature of the judiciary's role in this regard.
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The Declaratory Theory holds that judges do not make law but merely declare what the law has always been. On this view, when a court decides a case, it is identifying a pre-existing legal rule rather than creating a new one. This theory preserves the formal distinction between the legislative and judicial functions, but it is widely regarded as a legal fiction that obscures the creative role judges actually play.
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The Legislative Theory acknowledges that judges perform a significant law-making function, both through the development of the common law and through the interpretation of statutes. The development of the law of negligence following Donoghue v Stevenson [1932] is a frequently cited example of judges shaping the law in ways that have wide-ranging social consequences, a function that Parliament alone cannot realistically discharge on a case-by-case basis.
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The Judicial Restraint Theory posits that judges should refrain from developing the common law in areas that Parliament has addressed or has deliberately chosen not to address. Under this theory, the judiciary defers to the legislature in contested areas of social policy, leaving it to elected representatives to resolve those matters through the democratic process. This theory reflects a form of institutional self-discipline that acknowledges the limits of judicial legitimacy in a parliamentary democracy.
Parliamentary Sovereignty and Judicial Self-Limitation
The common law doctrine of parliamentary sovereignty constitutes a form of self-imposed limitation on the judiciary's power. Courts have consistently held that they possess no authority to strike down an Act of Parliament on the grounds that it conflicts with the common law or with some other legal norm. The judiciary accepts that Parliament can legislate to override any rule of judge-made law. This principle was dramatically illustrated by Burmah Oil v Lord Advocate [1965], in which the courts decided in favour of the claimant, only for Parliament to pass the War Damage Act 1965 to reverse the effect of that decision retrospectively. The episode demonstrated with particular clarity that Parliament can undo the effects of judicial decisions by legislation — including retrospective legislation — and that the courts regard themselves as having no power to resist such an exercise of parliamentary authority.
EU Law and the Power to Suspend Acts of Parliament
The picture described above requires an important qualification arising from the United Kingdom's former membership of the European Union. Notwithstanding the general principle that courts cannot strike down primary legislation, it was established — most notably through Factortame (No 2) [1991] — that courts do have the power to suspend or disapply an Act of Parliament that is incompatible with EU law. Where such incompatibility was established, the court's decision had the practical effect of invalidating the relevant statutory provisions in their application to the matters in dispute. This represented a significant, if constitutionally circumscribed, exception to the doctrine of parliamentary sovereignty, and one that was expressly acknowledged as such by the courts.
Following the United Kingdom's withdrawal from the European Union, this power to suspend or disapply primary legislation on EU law grounds no longer applies to new domestic legislation. Nevertheless, the episode remains constitutionally significant as evidence that parliamentary sovereignty, whilst the default constitutional position, is not necessarily an absolute or irresistible principle in all circumstances.
The Human Rights Act 1998 and Declarations of Incompatibility
A further, ongoing qualification to the courts' general deference to Parliament arises under the Human Rights Act 1998. Where a court finds that a provision of primary legislation is incompatible with a Convention right under the European Convention on Human Rights, it may issue a declaration of incompatibility. Critically, such a declaration does not invalidate the legislation — it remains in force unless and until Parliament chooses to amend or repeal it. However, a declaration of incompatibility creates very considerable political pressure on the government to revise the offending provision, and in practice it has frequently prompted legislative action. Belmarsh case [2005] provides a prominent example: the House of Lords declared that indefinite detention without trial under the Anti-terrorism, Crime and Security Act 2001 was incompatible with Convention rights, a declaration that led directly to the repeal of the relevant provisions.
The Human Rights Act 1998 has substantially increased the volume of politically sensitive litigation that comes before the courts. By incorporating Convention rights into domestic law, the Act requires judges to adjudicate upon matters — such as the right to life, freedom from torture, and privacy rights — that are inherently political in character. The tension between judicial and parliamentary authority in this sphere is likely to persist and to generate ongoing constitutional debate.
Politicisation of the Judiciary
The increased involvement of the courts in politically sensitive decision-making has given rise to concerns about the politicisation of the judiciary. These concerns manifest in two principal forms.
The first concerns the appointment of senior judges to chair public inquiries into matters of significant political controversy. When a senior member of the judiciary presides over an inquiry into, for example, the conduct of government or the causes of a public disaster, questions arise as to whether that involvement compromises the judge's apparent impartiality and whether it draws the judiciary as an institution into political affairs.
The second concerns the willingness of government ministers and backbench Members of Parliament to criticise individual judges publicly — in breach of the constitutional convention of mutual restraint — when they are dissatisfied with the outcome of cases involving, for instance, lenient sentencing in criminal matters or rulings favourable to applicants in human rights cases. Such public criticism risks undermining public confidence in judicial independence and erodes the constitutional principle that judges must be free to decide cases according to law without fear of political reprisal.
Checks and Balances between the Legislature and the Judiciary
Mutual Restraint and the Sub-Judice Convention
The system of checks and balances between Parliament and the courts relies, to a considerable degree, on the conventions described above. The sub-judice rule operates as a check upon Parliament's potential to influence judicial proceedings, while the convention against criticising individual judges serves as a safeguard for judicial independence. Conversely, the courts' traditional reluctance to invalidate Acts of Parliament serves as a form of judicial deference to the democratic legislature, preserving Parliament's role as the primary law-making authority.
Judicial Checks on Parliament: EU Law and the Human Rights Act 1998
Notwithstanding the doctrine of parliamentary sovereignty, the judiciary possesses meaningful mechanisms by which it may check the exercise of legislative power. As noted above, courts were empowered under EU law to suspend or disapply Acts of Parliament that were incompatible with EU obligations, and the court's determination in such cases had the practical effect of invalidating the relevant statutory provisions. Under the Human Rights Act 1998, courts retain the power to issue declarations of incompatibility in respect of primary legislation that conflicts with Convention rights. Although such declarations do not formally override parliamentary authority, they constitute a significant institutional check upon it — one that operates through the mechanism of public and political accountability rather than through direct legal compulsion.
The combined effect of these mechanisms is to produce a constitutional relationship between Parliament and the courts that is neither one of pure parliamentary supremacy nor one of judicial supremacy, but rather a nuanced and evolving system of mutual constraint, institutional respect, and shared commitment to the rule of law.