England's government is a constitutional monarchy. In this system, the monarch is the head of state, while the Prime Minister is head of Her Majesty's Government, which wields executive power.
The executive power technically rests with the monarch, but she only exercises this power through Her Majesty's Government, which consists of the Prime Minister and his or her chosen ministers. The British legislative body is the Parliament. Parliament consists of two houses, the House of Lords and the House of Commons, the former of which is either appointed or hereditary, and the latter of which is popularly elected. For more than a century, Prime ministers have come from the House of Commons, making them responsible to Parliament.