Conservative Boris Johnson has seen his lead over Ken Livingstone in the London mayoral race cut in half in the last week, according to a poll on Monday.

With less than three weeks to go before Londoners vote on May 1, Johnson's advantage over the Labour mayor has been cut to just six percent.

The YouGov poll in the Evening Standard put the Tory on 45 percent, six points ahead of the mayor on 39 percent. The last survey put Johnson on 49 percent, with Livingstone on 36.

Liberal Democrat Brian Paddick saw his share of the vote rise from 10 to 12 percent.

The mayor said the polls showed that the race was still wide open and appealed to new voters to back him.

"Every Londoner can now be sure their vote will count in this election," he said. "More than 350,000 Londoners will have a vote for the first time at this election and I particularly appeal to them to keep our city going forward."

Livingstone was due to visit a Sikh temple on Monday with Prime Minister Gordon Brown.

Johnson accused Livingstone of hypocrisy after the mayor published a list of famous supporters, despite repeated calls for rivals to avoid treating the election like "Celebrity Big Brother".

Livingstone's list of 20 supporters includes singers Damon Albarn and Billy Bragg, comics Jo Brand and Phill Jupitus and actors Prunella Scales and Emma Thompson.

It included messages of support from Labour activist and TV presenter Tony Robinson and comedian Arthur Smith.

"Livingstone says he wants to focus on policies and not celebrities and yet he does the opposite," Johnson's spokesman said. "Ken has said this election is not 'Celebrity Big Brother,' yet clearly he is now trying to cover up for his lack of new ideas."

Livingstone has repeatedly accused Johnson of lacking the gravitas needed for the role of mayor. At his campaign launch last month, the mayor said: "This election is not 'Celebrity Big Brother'. It is about incredibly serious issues."

* YouGov polled 1,031 Londoners online from April 9 to 11.