Exit polls show Conservative candidate Boris Johnson neck and neck with Labour's Ken Livingstone, who has been Mayor since 2000.

Electronic counting in London started at 8.30am, with constituency results expected from mid-afternoon.

The mayoral and London-wide results are expected to be declared early this evening.

advertisementPrime Minister Gordon Brown is facing pressure from Labour MPs for a change in direction after a nightmare at the polls which saw the party slump to its worst results for a generation.

With results in from 98 councils in England and Wales, the BBC put Labour's projected national vote share at just 24 per cent, trailing 20 points behind David Cameron's Conservatives on 44 per cent and beaten into third place by the Liberal Democrats on 25 per cent.

Labour's Ken Livingstone, who is seeking his third term in the hot seat, is facing his toughest challenge yet from Conservative candidate Boris Johnson.

Both candidates were out yesterday trying to secure last-minute votes with Livingstone taking to the streets of east London.

Mr Johnson, meanwhile, was in south London appealing to his supporters.

Victory for Mr Johnson would add considerable momentum to Tory leader David Cameron's quest to win power nationally.

Yesterday's YouGov poll showed Johnson ahead of Livingstone by 47 per cent to 53 per cent, indicating that the race to become the capital's leader is still too close to call.