The doctrine of separation of powers in UK’s constitutional arrangements

Subject: Law
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The doctrine of separation of powers is the cornerstone of modern democracies. The origin of the doctrine is attributed to Aristotle, who is recorded as being the first individual to consider the assignment of separate and distinct roles to various branches of the government. Later, other notable philosophers, particularly Montesquieu and Locke developed and refined the doctrine, consequently giving rise to the idea that a government ought to be divided into branches, each of which engages in some form of scrutiny over the others in order to ensure that the other branches were not exceeding or misusing their powers. Montesquieu, in his Spirit of Laws (1752), postulated that liberty cannot be achieved if the power of judging is not distinctively differentiated from the executive and legislative powers. The intention is guarding against tyranny and preserving liberty. However, even though the institutions are divided, there are still dependent on one another so that no power exceeds the other two.

This later development comprises of the definition of separation of powers that is, the allocation of particular responsibilities, duties, and functions to specific institutions whose competence and jurisdiction are clearly articulated. This separation is among the three main branches of the government, the Executive, Legislative, and Judiciary branches. The Legislature has the power of making and amending the laws of the land. The Parliament is the sovereign institution of making laws, and comprises of the Queen, the House of Lords and the House of Commons. The Executive has the power of executing and enforcing the rule of Law. The members include the Prime Minister, Cabinet Ministers, elected Members of Parliament, Civil Service, local authorities, armed forces, and the police. The Judiciary’s power involves settling disputes arising from the interpretation and enforcement of the law between the state and private individuals, state institutions, and between individuals. The Members of the Judiciary are nominated but cannot be removed at pleasure. The best possible form of government is one that is founded on the separation of these functions and duties. Thus, the doctrine of separation of powers becomes a core value of any system that seeks to ensure the liberty of its citizens, where each government’s branch is functionally independent of the other.

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The doctrine of separation of power, together with the principles of parliamentary sovereignty and rule of law, are fundamental components of the Constitution of the United Kingdom. It is vital to the principle of constitutionalism specifically prescribing the suitable distribution of the various powers and setting the limitations of the exercise of those powers by the various institutions. However, in a Constitution that is highly dominated by Parliamentary sovereignty, the emphasis is not on the creation of three separate governmental institutions, which operate in isolation of each other. Such an arrangement is technically unworkable as it would lead to legal and constitutional deadlocks. For example, the arrangement in the UK is one where the Executive proposes laws to be passed by Parliament, which, once they become Acts of Parliament, are upheld by the Judiciary. The Constitution creates a system where institutional powers are largely, but not completely separated with the existence of checks and balances that prevent abuse of power.

Incremental constitutional reforms have now created a Constitution that is characterized by two types of separation of powers in the united Kingdom, based on territorial jurisdictions; on the one hand, there is separation between Parliament and the European Union, and on the other, there is separation among the various bodies in the United Kingdom, as opposed to having Parliament’s sovereignty and a concentration of power at the centre. This is a system where checks and balances among the various organs of the government are a critical component and where each organ plays a crucial role of determining fundamental rights and the extent of government actions. This fundamentally describes the modern doctrine of separation of powers, which is more concerned with institutional decision-making processes and institutional expertise, but where rigid adherence to the distinctions is increasingly becoming difficult as human rights adjudication takes pre-eminence.

Within the British context, the context of balance is of paramount importance. For example, in relation to a balanced Constitution, Lord Irvine stated that the English Constitution is strongly characterized by a representation of a delicate balance. However, such a description maybe criticized as being too vague, which suggests that there is some objective hidden hand that holds the constitutional institutions in equilibrium or that the doctrine of separation of power contains a mystical virtue as a component of the constitutional law, which can be used as a yardstick for measuring the merits of institutional arrangements. These criticisms notwithstanding, the statement underlies the concept of checks and balances, which in effect creates a balance in the exercise of the different powers.

However, several institutions and concepts have historically posed challenges to the implementation of the application of separation of powers, particularly before the development of the Constitutional Reform Act, 2005. The first such challenge is the Office of the Lord Chancellor. This was due to the triple functions of the Lord Chancellor; Judge, Cabinet Minister, and Speaker of the House of Lords. The Office received heavy criticisms due to its threat to the independence of different organs of the Government. It was viewed as a mockery to Montesquieu’s thesis of a division and balance of power in the government’s institutions.

The power of the Lord Chancellor to sit as a judge was granted under the Appellate Jurisdiction Act 1876, which authorized the Lord Chancellor to sit in the House of Lords to hear appeals together with the Lords of Appeal in Ordinary. Sitting in the House of Lords, with the exception of issues concerning the government or which were overtly political, gave the Lord Chancellor the power to make and develop laws through the system of common law. The Lord Chancellor was also the head of the Chancery Division of the High Court. The Chancellor also advised the Crown on the appointment of some High Court judges and Circuit judges, while also personally appointing some district judges, tribunal chairs, and lay magistrates.

The Lord Chancellor’s functions in the Judiciary also included disciplinary as he had the power of dismissing some judges for misbehaviour or incapacity. This was in addition to having statutory power as a Cabinet Minister, with a voice in both the Legislature and Executive, thus combining the three branches in one person. However, even though there were advantages existing between this close collaboration between the Executive and the Judiciary through the Office of the Lord Chancellor, it still manifested a substantial breach of separation of powers, which needed to be aptly amended. It was seen as interfering with the constitutional role of the Judiciary in relation to the Executive, as well as to the judicial independence, if its head and the guardian of its independence was also a Cabinet Minister. In addition, it lessened the justifications for and relevance of an independent judiciary either as a description of the Constitution or as a Constitutional ideal. Currently, the Lord Chancellor is not the sovereign figure of the Judiciary, even though the office was retained. The Lord Chief Justice is the head of the Judiciary, and who is also the head of the Courts in England and Wales. The Lord Chief Justice has a higher authority in relation to influencing decisions that relate to the administration of the court system.

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An independent Judiciary is essential to the implementation of the doctrine of separation of power. Judicial independence has mainly been measured in relation to the relationship between the Judiciary and the Executive. The role of the judiciary in relation to the executive according to Lord Mustill, is asserting that the exercise of the powers is in accordance with the substantive law created by parliament, in addition to ensuring that the manner in which these powers are exercised is in conformity with the Parliament’s intentions of fairness. According to Lord Lloyd, the court’s powers only exceeded to as far as granting discretionary relief if a minister exceeds the powers conferred on him by Parliament but cannot be compelled by the court to implement an Act of Parliament.

The courts have been keen on implementing separation of power. For example, in R v Secretary for the Home Department, the appellant had been convicted of double murder and sentenced to the mandatory life sentence with the minimum term. The Home Secretary consequently raised the minimum term, which was appealed against. Lord Steyn stated that the decision of imposing a term of imprisonment on an offender should be carried out by the courts and not by the Home Secretary. A member of the Executive carrying out this function blurred the boundaries of the separation of powers, as well as breaching the appellant’s right of having their imprisonment term determined by a court of law. A distinction was made between a mandatory and discretionary life sentences in which sentence tariffs could be applied. The only applicable exception is the ancient power given to the Parliament of imprisoning individuals found to be in contempt of the Parliament.

Further, in Matthews v Ministry of Defence the court stated that the executive should not have the power of effectively deciding a case in in a manner that it could order the court to dismiss it. In this case, Matthews sought compensation from the Crown after suffering from asbestos-related injuries, which resulted from his service in the Royal Navy as an electrical mechanic. He alleged that the defendant acted negligently or in breach of its statutory duty by exposing him to asbestos in his service. In denying the claim, the ministry cited the Crown Proceedings Act 1947, which exempts the Crown from tortious liability from individuals who served in the armed forces. Even though the court stated that statutorily the Crown could do no wrong, the court should still be allowed to execute its powers without interference from the Executive in relation to determining the kind of cases it could adjudicate over, as this breached the principle of separation of powers.

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The development of the Constitutional Reforms Act 2005 introduced significant features into separation of powers between the various organs of the government, particularly between the Executive and the Judiciary. For example, the monarch was legally responsible of appointing judges. This raised concerns on whether the judiciary could really be independent if the appointment of judges is carried out by the Executive. The 2005 Act made two key changes that resulted in enhanced separation of powers between the Judiciary and Executive. First, it established a new appointment process for the justices of the Supreme Court through a selection committee. The committee’s members include president and deputy president of the Supreme Court and the members of the respective judicial appointment commissions/boards of England and Wales, Scotland, and Northern Ireland. The Act also resulted in the creation of a Judicial Appointments Commission, tasked with selecting new judges of the senior courts; the High Court and above. The implementation of these measures has effectively reinforced judicial independence.

Further, the 2005 act made provisions for the dismissal of judges in a manner that further protects their independence. Previously, judges could only hold office based on their ‘good behaviour’. Technically, this provision did not do much for the independence of the judges since what matters is the person who determines if the judge misbehaves and thus be removed from office. An important feature in the current system is where the Crown can dismiss a judge only as a result of a resolution of both Houses of Parliament, a significant constitutional check given to the Legislature, and probably then can a judge be dismissed on misbehaviour. Further, the 2005 Act provides for the tenure of office for the judges, which means that they cannot be summarily dismissed by the executive. However, the act also advances the ambiguity of removal from office of the Lord Chief Justice and senior judges, where they hold office based on good behaviour.

Another significant feature of the Constitutional Reform Act in relation to separating the powers and functions of the branches of government was the creation of the Supreme Court as the highest court of the land, replacing the House of Lords. Previously, the Law Lords were allowed to sit in the House of Lords where they could undertake legislative functions. Currently, the justices of the Supreme Court cannot participate in the activities of the House of Lords even though they automatically regain their position as members of the House of Lords if their membership existed prior to their appointment to the Supreme Court. This explicit and transparent separation of powers between the Executive and the Judiciary has consequently created more systematic and constructive engagements between the two government’s organs, especially through Parliamentary Select Committees.

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However, there exists an overlap in the functions of the Judiciary and the Legislature. The latter is primarily tasked with the creation of new laws. The former can also engage in the same practices through judicially created laws. The Supreme Court, in its adjudication of disputes brought before it, can create new laws, which remain binding on itself and to all the lower courts through the doctrine of precedent. Case law form a primary source of law, whose stability is dependent on the flow of recent decisions, the stock of the established legal precedents, as well as the weight attached to the precedents and jurisprudential trends. Therefore, the members of the Supreme Court create a quasi-legislative body whose interpretation and application of the law is binding.

Despite the numerous attempts at maintaining separation of power among the Executive, Judiciary, and Legislature, this doctrine has been termed as being cloudy in modern UK, where judicial independence in particular, still remains a matter of rhetoric. Essentially, the United Kingdom has developed various effective informal systems for the separation of powers, even though there is no general theory in existence. Nevertheless, the independence of the Judiciary has particularly enjoyed a certain respect as a principle of fundamental importance. The political culture in the United Kingdom is one that provides protection to the judiciary’s independence, but where there is a co-mingling of the three branches in the execution of their functions and responsibilities. The Constitutional Reform Act, 2005 has ensured a continuing and heightened the influence of the doctrine of the separation of powers as a fundamental constitutional principle.

The doctrine of the separation of powers is a significant principle that underlies virtually all constitutional arrangements, alongside other crucial principles, such as the Rule of Law and the Sovereignty of the Parliament. With origins from Aristotle, Locke, and Montesquieu, the doctrine works as a checks and balance strategy to ensure that each of the three governmental organs does not exceed or abuse the powers conferred on it. This ensures liberty and an effective and proper working of each organ. However, the branches do not work in complete isolation of each other, but are rather intertwined and harmonized even though they remain as independent entities, fulfilling distinct functions that are carried out in accordance with its own methods. This indicates that even though the branches overlap in some aspects, the unwanted repercussions of a complete fusion are avoided through a system of checks and balances, which makes each branch accountable to the other.

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  1. The Act of Settlement, 1700 (now repealed).
  2. The Appellate Jurisdiction Act, 1876.
  3. The Constitutional Reforms Act, 2005.
  4. The Crown Proceedings Act, 1947.

Case Law

  1. Matthews v Ministry of Defence [2003] HL 13.
  2. R (on the application of Anderson) v Secretary of State for the Home Department [2003] UKHL 46.
  3. R v Secretary of the State for the Home Department ex p Fire Brigades Union [1995] HL 5 APR.


  1. Alder, J., 2015. Constitutional and Administrative Law. Basingstoke: Palgrave Macmillan.
  2. Barnett, H., 2017. Constitutional & Administrative Law. London: Taylor & Francis.
  3. Carmichael, P., and Dickson, B., 1999. The House of Lords: Its Parliamentary and Judicial Roles. Hart Publishing.
  4. Cownie, F., Bradney, A., and Burton, M., 2007. English Legal System in Context. Oxford: Oxford Univ. Press.
  5. Gerangelos, P., 2009. The Separation of Powers and Legislative Interference in Judicial Process: Constitutional Principles and Limitations. London: Hart Publishing.
  6. Masterman, R., 2010. The Separation of Powers in the Contemporary Constitution: Judicial Competence and Independence in the United Kingdom. Cambridge: Cambridge University Press.
  7. Woodhouse, D., 2001. The Office of Lord Chancellor. London: Hart Publishing.


  1. Fon, V., and Parisi, F., 2006. Judicial Precedents in Civil Law Systems: A Dynamic Analysis. International Review of Law and Economics, Vol. 26.
  2. Mojapelo, P. M., 2013. The Doctrine of Separation of Powers. Forum, Vol. 26, No. 1: pp. 37-46.
  3. Morris, C., and Malone, R., 2004. Regulations Review in the New Zealand Parliament. Macquarie Law Journal, Vol. 4, No. 2.
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