Boris still has 10-point lead in race for City Hall

The latest YouGov survey puts the Tory candidate 10 points ahead, suggesting many Londoners continue to feel it is time for change.

It comes as David Cameron joined his candidate on the campaign trail for the first time today. The Tory leader hailed Mr Johnson as a "proper Conservative" with a practical mind as he attacked Mr Livingstone for "arrogance".

He said of the Mayor: "There appears to be very little focus at City Hall on the issues that really matter to London.

"He's completely lost touch with the people who once supported him. He's now effectively the Labour government's representative in London and you get the same arrogance and intolerance of criticism you associate with Gordon Brown."

Mr Cameron added that Mr Johnson had a "properly thought through" plan for the capital despite claims from the Mayor's campaign. The pair reiterated Mr Johnson's focus on cutting violent crime with Mr Cameron saying fear of attack was the biggest factor undermining quality of life in the capital.

Despite an overall 25 per cent drop in crime over the past five years, Mr Johnson said: "If you talk to people about their real experiences and look at the reality of what's happening in London it would be irresponsible not to take a stand."

Gordon Brown has also publicly endorsed Mr Livingstone but there have been reports the Prime Minister does not think victory is likely. However, Mr Johnson's lead has narrowed slightly, a sign that Mr Livingstone's relentless focus on the Tory's competence is beginning to have an impact.

The YouGov poll for the Standard has Mr Johnson two points down from a fortnight ago on 47 per cent, the Mayor remaining static on 37 per cent, Lib-Dem Brian Paddick on 10 per cent and Green Si‚n Berry on two per cent.

After allocating second preference votes, the Tory candidate leads the Mayor on 56 per cent to 44 per cent. Mr Livingstone has regained some momentum with plans for the environment and housing after allegations of corruption and cronyism.

Mr Johnson has also been pursuing his "below the radar" campaign in outer London where he stands his best chance of maximising the Tory vote.

The survey comes before an Evening Standard debate tonight where the main candidates will come face to face on the key issues of the campaign.

YouGov questioned a representative sample of 1,051 Londoners online between 20 and 25 March. A total of 17 per cent said they did know who to support, the same as in the last poll, suggesting there was still all to play for.

Mr Livingstone's vote, according to YouGov, has fallen from 44 per cent in January to 39 per cent in February and has remained static at 37 per cent since.

Mr Johnson's lead has crept up from 40 per cent to 44 per cent then 49 per cent, dropping to 47 per cent today, while Mr Paddick went up from eight to 12 per cent but is now down to 10 per cent.

In response to the findings, a spokeswoman for Mr Johnson said: "The only poll that matters is 1 May." The Tory candidate has also refused to reveal his senior team if he is elected but hinted he would recruit senior corporate figures. A spokeswoman for the Livingstone campaign admitted for the first time it would be "close" but claimed YouGov's findings were "wrong".

She argued the Mayor polled stronger in polls that do not use YouGov'smethod.

Home Secretary Jacqui Smith was today accused by Mr Johnson of "propaganda" for Ken Livingstone. Government newspaper adverts today promote "community policing", a central policy of the Mayor. Whitehall rules ban publicity that appears to promote one political party during an election.