<P> Originally, British elections took place over a period of several weeks, with individual constituencies holding polling on separate days . The Parliament Act 1911 introduced the requirement that elections in all parliamentary constituencies be held on the same day . There has been a convention since the 1930s that general elections in Britain should take place on a Thursday; the last general election to take place on any other weekday was that of 1931 . </P> <P> The five - year limit on the time of a Parliament can be varied by an Act of Parliament implemented by several bodies . This was done during both World Wars; the Parliament elected in December 1910 was prolonged to November 1918, and that elected in November 1935 lasted until June 1945 . The House of Lords has an absolute veto on any Bill to extend the life of Parliament . </P> <P> In U.S. politics, general elections are elections held at any level (e.g. city, county, congressional district, state) that involve competition between at least two parties . General elections occur every two to six years (depending on the positions being filled with most positions good for four years) and include the presidential election, but unlike parliamentary systems the term can also refer to special elections that fill out positions prematurely vacated by the previous office holder (e.g. through death, resignation, etc .). Some parallels can be drawn between the general election in parliamentary systems and the biennial elections determining all House seats, although there is no analogue to "calling early elections" in the U.S., and the members of the elected U.S. Senate face elections of only one - third at a time at two - year intervals including during a general election . </P> <P> Unlike parliamentary systems where the term is distinguished from by - elections, a general election in the US is used in reference to and distinguished from primaries or caucuses, which are intra-party elections meant to select a party's official candidate for a particular race . </P>

Who decides when a general election takes place