The opposition Conservative party, led by David Cameron, has consistently held an edge in recent opinion polls, but it is not clear that Cameron has a big enough lead to dislodge Brown.

Elections will take place on May 6.

Brown's Labour party has been in power for 13 years, first under Tony Blair and, since 2007, with Brown as prime minister.

Under the British parliamentary system, voters choose a member of parliament from each of 650 constituencies, or districts. The party with the most seats traditionally gets the first chance to form the new government.

Queen Elizabeth II, as head of state, formally dissolved parliament on April 12, a procedural step.

The announcement means there are officially no members of Parliament as of 5 p.m. London time Monday.

"Government ministers remain in charge of their departments until after the election result is known," according to Parliament, but do not make any major policy decisions.

The new parliament is due to take office on May 24.