Although the doctrine of separation of power plays a role in the United Kingdom's constitutional life, the constitution is often described as having "a weak separation of powers" (A. V. Dicey) despite it being the one to which Montesquieu originally referred. For example, 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). 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 most judicial disputes in the U.K. 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 U.K. is more accurately described as a "fusion of powers".