Unlike the US there is no maximum term of office for a UK Prime Minister, they could hypothetically remain prime minister until they die, just so long as their party maintains a majority of seats in the House of Commons. The maximum length of time between elections is five years, but the ruling party may call an election at any time before this.
In modern times a parliamentary election has generally been called once every four years, like America, although the last general election in May 2010 was the first in almost five years. But the absence of a restriction on the term of office has not necessarily always seen British prime ministers serve for longer than American presidents. This article takes a look at the five longest serving British prime ministers.