The race for London's next Mayor has officially begun.

Candidates including incumbent Boris Johnson and former Mayor Ken Livingstone are vying for the chance to lead London for the next four years - and to wave the flag at this year's London Olympics.

Some of the wannabe Mayors have already begun campaigning across London for the Mayoral election but today marks the official start of the campaign.

The seven who have already indicated their candidacy are Boris Johnson, Conservative; Ken Livingstone. Labour; Brian Paddick, Lib Dem; Jenny Jones, Green; Carlos Cortiglia, BNP; Lawrence Webb, UKIP; and Siobhan Benita, Ind.

Nominations for the fourth mayoral election since the post was created in 2000 are now open, and candidates' spending will be subject to strict limits until polling day. The starting pistol was also fired in the race for 25 seats on the London Assembly, also being elected on May 3.

About 5.8 million people are eligible to vote, but in 2008 fewer than half of them bothered to go to the polling station, with average turnout of 45.3% across London.