Londoners should "hold their nose" and support Ken Livingstone in the London Mayoral elections, according to Labour's campaign chief.

Tom Watson MP, the party's deputy chairman, acknowledged on Thursday morning that while Labour lead the Tories nationally in the polls, Boris Johnson is ahead of Livingstone in London.

But Watson, Labour's campaign co-ordinator, warned listeners of LBC radio that Johnson's victory would be seen as a "vote of confidence" in the coalition.

"Those Labour voters thinking of going to vote for Boris, hold your nose, vote for Ken... that's the way that you will help Labour" he added.

Watson was grilled about Livingstone's campaign pledge to cut transport fares, with a promise to save Londoners over £1000. In response to the claim that Livingstone's figures had not been fact-checked independently, Watson said: "Well I believe them".

When pushed for further reasons to vote for Livingstone, Watson said "He's got a beautiful dog."

"I shouldn't say this, but there is an American maxim that when a politician is in trouble, get him a dog" he added.

Following his appearance on LBC, Watson said there were a number of people who say that they would vote Labour if there was a general election tomorrow but are currently considering voting Conservative because they either like Boris Johnson or don’t like Ken.

"I was trying to say that it is important for our campaign to convince these people that even if they didn’t like Ken they should consider voting Labour because David Cameron would claim victory if Boris wins," he wrote on his blog.

"From what our campaigners on the ground say, the last thing this group want to do is give an endorsement to David Cameron."

He added: "There is a great picture of Ken and his beautiful labrador dog in today’s Guardian. That prompted me to crack the Harry Truman maxim about politicians and dogs."