The United Kingdom is a parliamentary monarchy-that is, the head of state is a monarch with limited powers. Britain's democratic government is based on a constitution composed of various historical documents, laws, and formal customs adopted over the years. Parliament, the legislature, consists of the House of Lords, the House of Commons, and the monarch, also called the Crown. The House of Commons is far more influential than the House of Lords, which in effect makes the British system unicameral, meaning the legislature has one chamber. The chief executive is the prime minister, who is a member of the House of Commons. The executive branch also includes Her Majesty's Government, commonly referred to simply as "the government." The government is composed of ministers in the Cabinet, most of whom are members of the House of Commons; government departments, each of which is responsible to a minister; local authorities; and public corporations. Because the House of Commons is involved in both the legislative and executive branches of the British government, there is no separation of powers between executive and legislature as there is in the United States.