Ken's game of catch-up fails to harden into winning lead

Seven out of 10 Londoners support the idea, in both inner London and the outer doughnut. More than half of rival Boris Johnson's supporters admit they like it.

The bad news for Ken is that less than half - 44 per cent - believe that Mayor Livingstone would actually keep his word once in City Hall. Cynicism about whether he would fulfil his pledge is highest among young voters aged 18 to 24, who are a key target group for Labour.

Ken's credibility question seems to be the main reason why the astonishing campaign momentum he achieved in January has been suddenly checked in February.

Today's poll puts the two great rivals roughly neck and neck again. A month ago, Ken had a two-point lead. Now Boris has a two point lead. That's within the margin of error for an opinion poll, so the two-point swing implied may just be an illusion.

What the headline figures do show, beyond doubt, is that Ken has failed to extend or harden his January lead. He is like a marathon runner who, in a stupendous effort, catches up with the leader only to find he cannot break ahead. Our survey by YouGov is packed with other insights about where the frontrunners stand.

In inner London, Ken is ahead by 53 per cent to 47. But the huge outer doughnut is sticking with Boris by 52 to 48. Among voters aged 18 to 24 the pair get 50 per cent each. Ken is somewhat ahead among 25 to 59-year-olds. But Boris has a massive "grey power" advantage, a two to one lead among the over-sixties.

On the four issues that matter most to Londoners, Ken is ahead on three. He has 15 and 16 point leads on improving transport and tackling the high cost of living, and a narrow three-point lead on creating jobs. On crime fighting, Boris is ahead by a slender four points. It goes to show that simple, bold pledges work best.

It is a bookmarkers' dream: a battle between two heavyweights that could go either way.

Boris is ahead by a nose. But with three months to go, the odds could change dramatically.