Comment: even the weather could make crucial difference

This is slightly down on the weekend poll in this series. However, there appears to have been a late surge of second preferences to Ken Livingstone which, when added in, close the gap - taking account of first and second preferences - to six points (53 to 47). He also appears to have attracted back more of his party's core vote.

But this is only a poll. Polls can be wrong. Actual votes are what counts. If there is a turnout today of above 43-44 per cent, Ken could still pull it off. Lower turnouts, say 38-39 per cent, would be a problem, even on the basis of earlier polls by other companies that were more favourable to him.

Neither side will wish their voters to believe this is anything other than a close race. Even the weather, which is forecast to be overcast and showery, could make a difference.

Have voters been galvanised by this contest? It is impossible to say yet. There has certainly been a massive amount of media coverage within the capital and worldwide. Labour, with their depleted activist base, need to convince the full Livingstone rainbow coalition to vote to save their man. London is such a vast place that neither of the major parties can provide comprehensive cover. Greater London Council turnouts occasionally rise to 44 per cent, though recent borough and GLA elections have been stuck below the 40 per cent mark.

All the polling has shown Boris ahead among older voters. This group is more likely to vote than any other. Electoral registration in London is also low, suggesting another potential difficulty for Ken. But Ken may yet prove to be worth relatively more votes than an unpopular Labour Party. His campaign, which he admitted himself yesterday had been inferior to the Tories', has run hard to the very end.

Interestingly, there have been no late polls from other organisations. Few elections in Britain have provided the polling companies with such spine-tingling pressure. While polls are not forecasts of results, it is inevitable there will be a post-mortem on the problems faced by the organisations who have polled opinion in this contest. They cannot all be right.

This year's mayoral contest has been an incredibly bitter one. The leading candidates have worn themselves ragged racing across the capital in an all-out chase for votes. Two-horse political races are prone to end up as a run to the wire. This is no exception. Many factors will influence the relatively small gap between the final tally of votes for Ken Livingstone and Boris Johnson. No election has ever provided Ken with such a challenge.

Today Londoners must decide between continuity and change. Turnout will be the key to the result.

Tony Travers is director of the Greater London Group at the London School of Economics.