The poll, which put the Tories 26 points ahead, added to the pressure on Gordon Brown a week after Labour suffered a devastating set of local election results and saw Boris Johnson become Mayor of London.

A YouGov survey put the Tories on 49 per cent and Labour on 23. The Liberal Democrats are on 17.

Labour's rating is thought to be the lowest the party has registered since such records began in the 1930s.

Mr Brown also faces losing the Crewe and Nantwich by-election in two weeks. If that happens, further questions would be raised about his leadership.

Party divisions have been exposed over Mr Brown's decision to scrap the 10p income tax rate. That is being blamed for Labour's dire showing in the local elections.

Labour's share of the vote was 24 per cent, putting them in third place behind the Tories (44 per cent) and the Liberal Democrats (25 per cent).

The Prime Minister has been involved this week in another damaging internal row. This time it was with Wendy Alexander, the leader of the Labour group in the Scottish parliament, over a planned independence referendum. It has again led to questions about his authority.

Charles Clarke, a former Cabinet minister, told Mr Brown not to engage in "dog whistle" politics.

The YouGov poll, however, indicates that Labour's position would not improve with another leader in charge.

Potential successors such as Ed Balls, David Miliband, Jack Straw, Harriet Harman, Andy Burnham, Alan Johnson and James Purnell would all make things worse, the poll suggests.