Boris 'ahead by 10pc' according to poll which predicts he will unseat Red Ken as mayor

With just two days before voters choose who they want to run the capital, the survey predicted a 55-45 per cent victory for the Tory candidate.

But almost one in seven Londoners have yet to make up their minds - and late decisions could still sway the outcome on Thursday.

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"The election remains finely balanced," Mr Johnson warned yesterday.

"The next few days are the most critical."

The findings in a YouGov poll for London's Evening Standard newspaper came as the Tory front-runner put crime at the centre of his campaign.

He highlighted an independent study showing street violence at a five-year high, with 43 per cent of Londoners believing they or their family were in immediate danger.

The vast majority - 85 per cent - blamed Mr Livingstone.

Separate figures obtained by the Johnson campaign, and seen by the Daily Mail, show that there are five reported rapes in London every day.

Official Scotland Yard records show that there were 8,766 sexual offences - one an hour - in 2007-08, including 1,919 rapes.

Mr Johnson admitted during a TV interview yesterday that he had once tried to take cocaine - or at least something he had been told was the Class A drug.

The Tory candidate, who has admitted smoking cannabis, has long been at the centre of a mystery over whether he used cocaine while a student at Oxford.

He has said in the past: "I think I was once given cocaine but I sneezed so it didn't go up my nose. In fact, it may have been icing sugar."

Yesterday he told Sky News: "I once abortively, and I stress abortively, attempted what I was told was cocaine.

"I have no idea whether it was or not because I'm afraid none of it produced any effect on me whatever."

Earlier in the campaign, Mr Livingstone was involved in a wrangle over drugs when the Green Party, with whom he has an electoral pact, backed a call to legalise Ecstasy.

In a message to voters yesterday, Mr Johnson said: "It is time to hold Ken Livingstone to account. If he wins on Thursday it is another four long years of waste, deceit, scandal, cronyism, crime and congestion."

Mr Livingstone is focusing on transport and his message that Mr Johnson is not up to running a city.

London is the top prize in a swathe of local elections across the country.

If Labour fails to hold the capital and suffers heavy losses elsewhere it will further undermine Gordon Brown's premiership.

According to the YouGov findings-Mr Johnson is 11 points ahead of Mr Livingstone on first choice votes - 46-35 per cent - and a point ahead of his Labour rival on the crucial second preferences.

It means that, in a straight run-off, the Tories' man wins 55 to 45.

Such is the dogfight now raging that Mr Johnson yesterday accused Mr Livingstone's supporters of "dirty tricks".

They included adverts claiming that pensioners' free travel on public transport - the Freedom Pass - was under threat.

A Johnson spokesman said of the transport claim: "It is a measure of the mayor's desperation that he is being driven to frighten elderly people.

"The Freedom Pass is 100 per cent guaranteed."

The bruising nature of the battle proves just how crucial the result will be in a national context.

Mr Brown has been urged to stay away, amid suggestions that he could damage Mr Livingstone's hopes, but Tory leader David Cameron was in London yesterday.