Heads of State and Government

The U.S. and U.K. political systems differ at the highest levels. In the U.K., the head of state and head of government are different roles. The reigning monarch -- Queen Elizabeth II, as of 2014 -- is the head of state responsible primarily for ceremonial duties. She orders the lowering of the Union Jack to half-staff when appropriate, delivers the Speech from the Throne and speaks to the British people during major crises. The head of government -- the person responsible for day-to-day management of the government -- is the prime minister. In the United States, the president assumes both positions, and carries out responsibilities similar to the combined duties of the queen and prime minister.

Formal Constitutions

The Constitution -- penned in 1787 in Philadelphia and ratified by 1790 -- is the supreme law of the United States. The U.K. has no formally written constitution. Instead, what may be referred to as its constitution is the entire body of its laws and principles that deal with regulating the populace and running the government. Parts of this regulatory body, such as the Parliament Act of 1911, are statutory and written, but others are simply known through tradition and historical precedent.

Legislative Bodies

The U.S. has a Congress, with a Senate and a House of Representatives that are completely separate from the executive and judicial branches of government. In the U.S. system, each of the three branches of government acts as a check and balance on the others. Both the House and Senate are elected bodies, and their powers are outlined in the Constitution

The British have a Parliament, with the upper House of Lords and the lower House of Commons. Members of the House of Commons are elected by their constituencies, and the leader of the dominant party in Commons is appointed by the queen to be prime minister. The House of Lords is an unelected body of peers that can check the power of the Commons by reviewing and amending bills. Before 2009, Britain had no supreme court, and the House of Lords also acted as the final court of appeal.

Political Parties and Elections

While the U.S. has two major political parties that dominate the country's politics, British politics has a multitude of parties representing diverse constituencies. Elections in the two countries also vary, with most U.S. federal elections happening on a regular schedule: The president is elected every four years, senators every six, and congressional members every two. Previous to 2011, general elections in Britain were not fixed. With the passage of the Fixed-term Parliaments Act 2011, Parliament is required to hold elections every five years, beginning in 2015. However, elections may occur before the five-year schedule if the House of Commons passes a vote of no confidence.