Boris Johnson pledged yesterday to sweep away the "superannuated Marxist cabal" installed at City Hall by Ken Livingstone, as he launched his campaign to become Mayor of London.

The Tory candidate let himself off his self-imposed leash temporarily as he launched a tirade against the advisers appointed by Mr Livingstone, who has been accused of surrounding himself with friends and cronies on the public payroll during his eight years as Mayor.

The capital votes a month today and there are growing jitters in Labour circles that Mr Johnson could score a famous victory which would boost Tory hopes of repeating his "time for a change" message at the general election.

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But you have to look hard for evidence that Mr Johnson is the Tory candidate on his campaign material. Outriders with "Back Boris" umbrellas mapped the way to his launch, on a council estate in Edmonton, north London. His newsletter describes him as "mayoral candidate Boris Johnson" and the only use of the word "Conservative" on the front page was in indecipherable light grey. Vote for the Boris Party was presumably the message.

An overflowing Bounces Road Community Hall was not natural territory for Mr Johnson and his special guest David Cameron, who got the film star treatment, engulfed by TV cameras and photographers, when he went to the podium.

The venue was a long way from Eton and Oxford, where the two men were contemporaries. But a bridge was provided by Ray Lewis, a former prison governor who set up Eastside Young Leaders' Academy because he was appalled by how many black youngsters ended up in prison. He called for change in London after a spate of murders and was proud to introduce the man he called "my mate Dave".

Mr Cameron said the mayoral contest was "vital" for Londoners. He took a slightly more emollient line towards Mr Livingstone than his man Boris, reflecting the opinion polls that show people may have tired of "Red Ken" but do not hate him. "He did some good things," said Mr Cameron, but he was now the Labour Government's representative in London. In contrast, he added: "I don't always agree with Boris, but I respect the fact that he is his own man."

The venue was chosen in part to answer claims that Mr Johnson was campaigning in the "leafy suburbs" in a "doughnut strategy" that missed out the middle. There were not many leaves about yesterday. The other reason was that four of the 11 murders of young people in London this year have been in this area. Tory strategists are in no doubt that crime is "the number one issue" on the doorsteps.

"When you have 27 teenagers being stabbed or killed last year and another 11 this year, it is not as if they were all individually victims of a series of freak events," said Mr Johnson. "These deaths are the culmination and the symptoms of something that is going badly wrong in our society."

Who else is in the Boris Party is a good question. Mr Johnson was coy about the advisers he would install, if he becomes Mayor, to replace the "superannuated Marxists". This is dangerous territory because it implies he would need minders to keep him on the straight and narrow.

A YouGov survey for the London Evening Standard gives Mr Johnson a 10-point lead. He is on 47 per cent (down two points), Mr Livingstone on 37 per cent (no change) and Brian Paddick, the Liberal Democrat candidate, on 10 per cent (down two points). On second preferences, which could decide the election because people have two votes, Mr Paddick is on 43 per cent, Mr Johnson 18 per cent and Mr Livingstone 14 per cent.