Comment: Ken's an extraordinary survivor - it will go to the wire

This week sees the official start of the mayoral election campaign. Despite weeks of skirmishing, Ken Livingstone, Boris Johnson and Brian Paddick are still in the foothills of the struggle that lies ahead. In the days and weeks ahead, manifestos will be launched, further allegations of various kinds made and a book (about Livingstone ) published. London faces a real choice.

Today's new opinion poll suggests a gap is opening up between the Tory challenger, Johnson, and the incumbent, Livingstone. YouGov has now undertaken three full-scale polls which, together, imply the Mayor has serious problems as he faces the final six weeks before the election.

His vote, according to YouGov has fallen from 45 per cent in December to 39 per cent in February to 37 per cent today. Johnson, by contrast, has moved up from 44 to 49 per cent. Lib-Dem Paddick, now running at 12 per cent, is up from seven per cent in December. The Labour Party was recently so spooked by polling evidence suggesting Johnson might win that it released some of its own polling (by MORI) that showed Livingstone ahead. But the news from Labour's poll was not as good as it looked. Of those certain to vote, including first and second preferences, Livingstone was only two per cent ahead of Johnson.

The problem here is that when similar polls were conducted in the run-up to the 2004 election, Livingstone was well ahead of Tory Steve Norris, typically by 15 to 20 percentage points. A two per cent lead looks paltry by comparison.

Of course, opinion polls are not real votes. The hard campaigning is about to begin. Livingstone remains one of the best tactical politicians in Britain and his staff have recently been battering Johnson over the apparently minor issue of the cost of re-introducing bus conductors if a new generation of Routemasters were to replace bendy buses.

It is clear Labour's detailed polling shows that Johnson is vulnerable to charges of "incompetence" and "inexperience". Expect more challenges to his grasp of detail and of his capacity to govern in a crisis.

But Livingstone has a number of serious problems of his own. The first is the Labour Party's current misery. Yesterday's papers published polls that suggest Labour is now deeply unpopular. Gordon Brown is a millstone around the Mayor's neck.

How Livingstone must wish he were an Independent, as he was in 2000. Second, it now appears that the handling of the Lee Jasper affair has dented the Mayor's reputation. In particular, week after week of allegations and denials have poisoned the national media's view of the City Hall regime.

Finally, the Mayor and his senior officials have displayed clear evidence of "headless chicken syndrome". This has been most obvious when, for example, Livingstone has been seen screeching "hypocrites" at the Assembly or during ill-judged TV appearances by members of the Mayor's Office.

The difficulty with all this aggression is that it damages the "Cuddly Ken" image that has been nurtured over many years. The evolution of the Grumpy Old Mayor's Office has not been a pretty sight - nor is it helpful electorally. Livingstone needs to come up with new policies to challenge the "fatigued" label that Johnson's spin doctor, Lynton Crosby, will be pinning on him. But before the Johnson campaign cracks open the champagne, they too have problems.