The United Kingdom is a constitutional monarchy, with executive power exercised on behalf of the Queen by the Prime Minister and other cabinet ministers. The Prime Minister is chosen as the MP who can command a majority in the House of Commons " usually the leader of the largest party. The current Prime Minister is David Cameron of the Conservative Party, who has been in office since 2010. Parliament is the national legislature of the United Kingdom. It is composed of the elected House of Commons and the unelected House of Lords, whose members are mostly appointed. The House of Commons is more powerful of the two houses. It has 646 members who are directly elected from single "member constituencies based on population." The House of Lords has 724 members constituted of Lords Temporal and Lords Spiritual. Since the 1920, the two largest political parties in British politics have been the Labour Party and Conservative Party. The Liberal Democrats are the third major party in the UK Parliament. In the United Kingdom the monarch has extensive theoretical powers, but his or her role is mainly ceremonial. The monarch is an integral part of Parliament (as the ˜Crown-in-Parliament'), summons Parliament and theoretically gives it the power to create legislation. An Act of Parliament doesn't become law until it has been signed by the Queen (being given Royal Assent), although no monarch has refused to assent to a bill since 1708. Although the abolition of the monarchy has been suggested several times, the popularity of the monarchy remains strong in spite of recent controversies. .
The Prime Minister is the most important person in British politics but the highest authority of the executive, judicial, and an integral part of the legislative branch is a hereditary monarch. When determining powerful of the Prime Minister we should mention about the relationship with the Monarch.