Analysis by the Press Association of the few comparable council by-elections this month suggests little movement between parties since most of the seats involved were last fought in 2004. Then a BBC survey put Tories 11% ahead of Liberal Democrats with Labour 1% further behind in third place.

Even if Labour is trailing by as much as the 18% shown in the Daily Telegraph's YouGov poll, the scope for sweeping gains in seats and control are limited, with party activists struggling for every vote they can get.

The most fiercely-fought battle is that for London Mayor, where opinion polls have been consistently giving the lead to Tory challenger Boris Johnson over incumbent Labour's Ken Livingstone - although some margins have been small.

Any success for Mr Johnson may not extend to the Tory performance in the London Assembly elections where Liberal Democrats have a chance of winning their first-past-the-post seats at Lambeth and Southwark from Labour and South West from Conservatives.

Results from the capital will not be through until Friday afternoon and evening. A clearer indication of the national mood will come from results of 159 council elections outside London.

They are for 23 English unitary authorities - including four new ones at Cheshire East, Cheshire West and Chester, Durham and Northumberland, 36 big city and conurbation metropolitan districts, 78 English non-metropolitan districts and 22 Welsh councils.

In all except the Welsh councils and eight of those in England, only some of the councillors are up for election this year - restricting the gains prospects compared with 2007 when Tories took more than 900 extra seats.

Despite Conservatives' lead in 2004, Tony Blair went on to win a General Election less than a year later, although with a reduced majority.

If Labour did manage a net gain against the Tories on May 1 - for the first time at council elections since 1996 - Gordon Brown might see an opportunity to go to the country in 2009. But if Conservatives make the advance it would signal a long haul to the wire in 2010.