Boris Johnson's battle to hang on to his job as Mayor of London entered a crucial phase today as the race for City Hall heated up.
The Conservative mayor is locked in a tight contest with his Labour rival, although Ken Livingstone's election campaign was dealt a new blow this afternoon with an opinion poll giving Boris Johnson a clear lead.
It is the first sign of a breakthrough by the Conservative mayor since recent surveys put the two front-runners neck and neck.
Polling by YouGov puts Johnson on 49%, Livingstone on 41% and the Liberal Democrat Brian Paddick on 5%.
If the results are reflected on polling day, the winner will be decided by second preference votes. YouGov suggests the outcome would be a Johnson victory with 54% of the votes to Livingstone's 46%.
Livingstone's chances may have been damaged by recent disclosures about his tax affairs, although Livingstone still denies that this is a problem.
Livingstone, who is promising to cut tube and bus fares by seven per cent, camped with his dog Coco outside a north London underground station this morning talking to potential voters.
Johnson spent the first day of the formal election period visiting the outer suburbs, regarded as the heartland of his core vote. Here he told people at an engineering firm just what he found when he took over office from Ken Livingstone in 2008.
The issue of travel cost seems to already be the main focus for the battle to City Hall. Ken Livingstone has promised to bring down the cost of travel, but the Lib Dem candidate Brian Paddick thinks the former mayor is being unrealistic.
Jenny Jones, the candidate for the Green Party says that they will cut fares as well as investing in transport, insisting that it does not have to be one or the other.
A number of independents are expected to stand along with candidates from UKIP and the BNP but this is essentially a two-horse race between Johnson and Livingstone - the current mayor and the former mayor.
Livingstone's recent poll boost may have been harmed by disclosures about his tax affairs.
In an increasingly bitter battle, the Tories hope to portray Livingstone as a tax dodger and hypocrite while Labour accuses Johnson of being lazy and out of touch with ordinary voters. The election takes place on May 3rd. The prize for the winner is the chance to run London for four years and a role in the closing ceremony of the Olympic games.