Boris takes lead in closest ever race for City Hall

Our exclusive YouGov poll today shows a dramatic turnaround from last month, with the Mayor now ahead by a super-slender 51 to 49 per cent margin.

With 80 days before voting and a two per cent margin of error in any poll findings, it means the May 3 result is too close to call and neither rival can afford a slip-up.

Tony Travers of the London School of Economics said: "This is going to be the tightest mayoral race we've had. This is a fight worth taking seriously if you're a voter. It's a decision that will affect Londoners' lives in a big way over the next four years."

He added: "The poll shows the pivotal issue now is high-spending Ken versus lower spending Boris. The election comes down to a choice between Ken's expansionist 'I'm spending money view' and Boris's 'I'm efficient and saving money' view.

The figures mark an end to the dramatic "Ken surge" that saw Mr Livingstone sprint from an eight-point deficit last year to a 51-49 lead in mid-January, shortly after an increase in Tube and bus fares. Mr Livingstone's promise to cut fares was the secret of his comeback. The promise was approved by 68 per cent of Londoners with more than a third naming it the one election pledge so far that most appealed to them.

However, the survey of 1,106 Londoners found that fewer than half the voters, 46 per cent, think Mr Livingstone would fulfil the promise.

If the mayoral vote was held tomorrow, some 46 per cent of voters say they would back Boris Johnson in the first round, which is one point ahead of Mr Livingstone's 45 per cent share, not enough for an outright win.

Brian Paddick, the Liberal Democrat former police officer, trails in third place with just six per cent and would be knocked out of the race. In the final run-off Mr Johnson would win by two points. Improving transport and tackling crime are the most important issues to voters.

Mr Livingstone is ahead by three-to-two on transport, while Mr Johnson has a small 32 to 28 per cent lead on crime.

The former mayor has a clear lead on cutting the cost of living, and a modest lead on creating jobs, which are third and fourth places in the list of voters' priorities.

"Boris and Ken are essentially neck-and-neck" said YouGov associate director Anthony Wells. "Ken's pledge to reduce bus fares links into what Londoners consider to be the most important issuing facing the capital, is simple to understand and has very strong support.

"What limits its effectiveness is that people are split over whether Ken would actually deliver it." Tessa Jowell, a key Livingstone campaigner, said: "This poll shows the race for Mayor is wide open. Crucially, people support Ken's fares pledge and trust him." A Johnson campaign spokesman said: "We do not comment on polls."

Mr Travers said: "Ken tends to be better on questions about who Londoners want to run a service. That suggests he is seen as the more effective candidate. But Boris's personality wins over a share of the voters.

"This poll shows that Boris has to come up with something on cost of living. This poll puts an enormous amount of pressure on both candidates not to slip up."