David Cameron makes 11th hour for potential Tory voters not to assume London Mayoral battle is already won

Pollsters predict the London Mayor, Boris Johnson, left, will beat his Labour rival, Ken Livingstone in today's mayoral election (Reuters)

David Cameron made an eleventh hour plea to potential Tory voters in London yesterday not to assume that the epic battle between two of the best known names in British politics is already over.

The pollsters and the punters believe that Boris Johnson will buck the national trend today and defeat Ken Livingstone in the long running and sometimes bad tempered London mayoral election.

Privately, both Conservative and Labour party managers agree that Johnson has probably pulled off a personal victory - though the government's unpopularity will mean that he will have to spend four years struggling with a Labour-controlled London Assembly.

But yesterday the Prime Minister to delivered a public warning to supporters to take nothing for granted.

“The most important message to Londoners is ‘don’t believe the bookmakers, don’t believe the opinion polls, make absolutely sure you go out and vote for Boris on Thursday,” he said in an interview with the Evening Standard.

In any normal election, the candidate who has received the Prime Minister’s unqualified support would rush to spread the news. But in the topsy-turvy London mayoral race, the first person to pick up and run with Mr Cameron’s words was Ken Livingstone, who could not wait to tell possible Labour voters that Cameron is backing his rival.

He issued a statement saying: “The David Cameron-Boris Johnson love-in on the eve of the election clarifies the very serious stakes for Londoners. It is two Tory peas in a pod. The Tory PM wants you to vote for the Tory Mayor so that they can keep going with Tory policies that mean recession, fare rises and police cuts.”

His statement illustrates what Tory MPs are privately calling the ‘lose-lose’ position that David Cameron faces. If – as expected - Boris Johnson secures another four year term as London Mayor, it will be seen as a personal victory secured during a slump in Conservative Party fortunes, raising Johnson's political standing at Cameron's expense. But if he loses, Cameron will get the blame, and his rival will be on the loose waiting for a by election that will give him the chance to get back into Parliament.

Meanwhile, the Labour leader, Ed Miliband, will be dreading the news that Livingstone has lost, because it will knock the shine off the hundreds of gains Labour is expected to make in council elections across the country - though a Livingstone victory will have its down side for the Labour leader too. It would mean that the newly elected Mayor, with his long record for whipping up controversy by voicing highly contentious views, would overnight become the most powerful labour politician in the land.

Whatever the outcome, the election will be remembered as a titanic struggle between two big personalities whose rivalry turned very personal one day when, in the semi-privacy of a crowded lift, an exasperated Boris Johnson let fly a sequence of obscenities as he accused his challenger of telling lies.