Great Britain most likely uses a parliamentary system of government.
In a parliamentary system of government, the citizens elect the legislature, which then decides who their chief executive will be. This is known as a parliamentary system of government. In this type of system, the chief executive, also known as the prime minister, is the leader of the party with the most members in the legislature. The Prime minister is appointed by the monarch but he is accountable to the legislative body, and could be removed by a vote of no confidence by the legislature.