Boris: City Hall win would put Tories on the road to No10

The Tory mayoral candidate said City Hall would be a "fantastic platform" for an election victory for David Cameron.

He told activists at the party's spring conference in Gateshead that the election was "the most important staging post" on the route back to No10.

Just days before the campaign begins officially next week, Mr Johnson said: "It is a tremendous opportunity for the Tories to gain momentum and show the tide is turning away from tired Labour administrations.

"To my mind London is, and always has been, one of the greatest cities on earth. But for the past few years it hasn't been a great place for all Londoners to live in. I think that is largely down to the impact of Ken Livingstone and the Labour government. I want to win this election and demonstrate how different life can be under a modern Conservative government."

A Tory win in London would be a huge boost to Mr Cameron and would be the first serious sign that the tide was turning nationally to the Tories.

It would be highly damaging for Gordon Brown if Labour lost London, with many London Labour MPs privately fearing they would lose their seats.

However, some Tory Central Office insiders still have concerns that Mr Johnson is not seen as a sufficiently serious candidate by Londoners to win.

If he does beat Mr Livingstone, they are worried that his administration, if not properly led, could have a detrimental effect on the party's chances.

But Mr Johnson insisted in his speech that he "truly believed" only he was able to offer Londoners a better deal than they get under Mr Livingstone.

Setting out his plans for the capital, he said he would constantly be looking to improve public services including transport, housing and policing.

He is relying on activists to boost the vote in traditionally blue outer London boroughs, which could make all the difference to the final result.

Meanwhile, the Mayor launched yet another attack on his Tory rival's transport plans, claiming there was a £20 millionhole in his plans for 440 more PCSOs.

Mr Johnson has pledged to use money earmarked for advertising and press officers to double the strength of safer transport teams on the buses.

He says he based his £84 million figure on a draft TfL budget in December which was then revised downwards to £63 million, but only this week.

But his rival's aides say TfL published a revised figure of £71 million in January - a month before Mr Johnson's pledge.

Mr Livingstone said the Tory candidate's plans were in "meltdown". "Boris Johnson's transport manifesto is unravelling. It is completely uncosted and must be withdrawn," he said.

"A new document with honest, accurate costs must be issued so Londoners can know what he is presenting to them."

However, Mr Johnson dismissed the claims as "a cynical plot" to distract attention from the Mayor's own failings.

He said: "This comes the day after it was revealed he misled Londoners over the extra police officers he promised.

"At the end of the day I care about police officers more than press officers."