<P> Although the doctrine of separation of power plays a role in the United Kingdom's constitutional doctrine, the UK constitution is often described as having "a weak separation of powers" A.V. Dicey, despite its constitution being the one to which Montesquieu originally referred . For example, in the United Kingdom, the executive forms a subset of the legislature, as did--to a lesser extent--the judiciary until the establishment of the Supreme Court of the United Kingdom . The Prime Minister, the Chief Executive, sits as a member of the Parliament of the United Kingdom, either as a peer in the House of Lords or as an elected member of the House of Commons (by convention, and as a result of the supremacy of the Lower House, the Prime Minister now sits in the House of Commons) and can effectively be removed from office by a simple majority vote . Furthermore, while the courts in the United Kingdom are amongst the most independent in the world, the Law Lords, who were the final arbiters of judicial disputes in the UK sat simultaneously in the House of Lords, the upper house of the legislature, although this arrangement ceased in 2009 when the Supreme Court of the United Kingdom came into existence . Furthermore, because of the existence of Parliamentary sovereignty, while the theory of separation of powers may be studied there, a system such as that of the UK is more accurately described as a "fusion of powers". </P> <P> Until 2005, the Lord Chancellor fused the Legislature, Executive and Judiciary, as he was the ex officio Speaker of the House of Lords, a Government Minister who sat in Cabinet and was head of the Lord Chancellor's Department which administered the courts, the justice system and appointed judges, and was the head of the Judiciary in England and Wales and sat as a judge on the Judicial Committee of the House of Lords, the highest domestic court in the entire United Kingdom, and the Judicial Committee of the Privy Council, the senior tribunal court for parts of the Commonwealth . The Lord Chancellor also had certain other judicial positions, including being a judge in the Court of Appeal and President of the Chancery Division . The Lord Chancellor combines other aspects of the constitution, including having certain ecclesiastical functions of the established state church, making certain church appointments, nominations and sitting as one of the thirty - three Church Commissioners . These functions remain intact and unaffected by the Constitutional Reform Act . In 2005, the Constitutional Reform Act separated the powers with Legislative functions going to an elected Lord Speaker and the Judicial functions going to the Lord Chief Justice . The Lord Chancellor's Department was replaced with a Ministry of Justice and the Lord Chancellor currently serves in the position of Secretary of State for Justice . </P> <P> The judiciary has no power to strike down primary legislation, and can only rule on secondary legislation that it is invalid with regard to the primary legislation if necessary . </P> <P> Under the concept of parliamentary sovereignty, Parliament can enact any primary legislation it chooses . However, the concept immediately becomes problematic when the question is asked; "If parliament can do anything, can it bind its successors?". It is generally held that parliament can do no such thing . </P>

Who advocated the theory of separation of powers