Contest that pits city against the suburbs

The mayoral election has revealed London to be a divided city, with support for Labour concentrated in the inner London boroughs and the Conservatives dominating the suburbs.

Analysis by the polling company Ipsos MORI found remarkably similar levels of support for Labour's Ken Livingstone and the Tory candidate, Boris Johnson, in their respective inner- and outer-London strongholds. The figures mean that next Thursday's contest could be decided by the two main parties' ability to persuade their natural supporters to turn out.

Although Tory officials deny it, Mr Johnson has been accused of pursuing a "doughnut strategy" in which he focuses his £1m campaign on the leafy suburbs. He has promised that he would be a mayor for "greater London" who would represent the city from public transport zones "six to one". The Tories accuse Mr Livingstone of being an "absentee mayor" in the suburbs.

The Ipsos MORI analysis shows why the Tories might be tempted to concentrate their fire on their heartlands. In the outer boroughs, Mr Johnson is on 45 per cent to Mr Livingstone's 36 per cent, among those who say they are certain to vote.

In inner London, the tables are turned. The incumbent is on 48 per cent and his Tory challenger 34 per cent.

When first and second preference votes are combined, Mr Livingstone is ahead by 58 per cent to 42 per cent in inner London, with Mr Johnson holding a 10-point lead in outer London. Overall, the figures point to a 50-50 split.

Although the divide was a factor in Mr Livingstone's victories in the 2000 and 2004 mayoral contests, the latest analysis suggests that it may have widened. Outer London boroughs have accused the Government of skewing its grants in favour of inner London and ensuring higher levels of public investment there. Labour has fared badly in borough council elections in the suburbs, with the Tories taking control in Bexley, Harrow, Croydon, Ealing, Hillingdon and Havering last year.

Other polls have shown people living in inner London are more satisfied with their area than those in outer London, where residents complain about creeping "urbanisation" and problems such as congestion and antisocial behaviour.

Senior Labour figures fear the row over Gordon Brown's decision to abolish the 10p tax rate could jeopardise their attempt to mobilise their core vote. "It is the only national issue to feature," one said.

Labour fears that some supporters will abstain. It is working hard to "get out the vote" in its strongholds and making a strong appeal to ethnic minority voters.

A separate survey by Ipsos MORI for the trade union Unison put Mr Livingstone on 41 per cent, Mr Johnson on 38 per cent, Mr Paddick on 12 per cent and Ms Berry on 3 per cent. After second-preference votes were reallocated, Mr Livingstone was on 53 per cent to Mr Johnson's 47 per cent. Mr Livingstone was regard as more trustworthy by 41 per cent and Boris Johnson by 30 per cent.

A Livingstone spokesman said: "This poll shows that after weeks of debate Londoners are considering the stakes for them in this mayoral election and, while the contest remains close, Ken Livingstone is moving into a clear lead. The difference between all voters and those certain to vote shows the more people use their vote the more likely it is that Ken Livingstone will win."