Tony Blair, the Labour Party's most successful election winner, told his party on Wednesday that it could not win power in Britain by lurching to the left.

Labour, which in May suffered its worst election defeat since 1987, is trying to select a new leader but has split over its future direction.

"You win from the centre, you win when you appeal to a broad cross section of the public, you win when you support business as well as unions, you don't win from a traditional leftist platform," former prime minister Blair said in a speech in London.

Blair won three elections in a row from 1997 to 2007 on a centrist "New Labour" platform.

A YouGov poll published on Wednesday showed left-wing candidate Jeremy Corbyn, who had previously been regarded as an outsider, could become the party's next leader.

The poll of 1,054 people eligible to vote in the contest showed support for Corbyn at 43 per cent, with the party's health spokesman Andy Burnham on 26 percent and its home affairs spokeswoman Yvette Cooper on 20 per cent. Liz Kendall, considered the Blairite candidate, was on 11 per cent.

"I wouldn't want to win on an old fashioned leftist platform ... even if I thought it was the route to victory, I wouldn't take it," said Blair.

"Move on but don't for heaven's sake move back. If we do then the public won't vote for us ... because our thoughts are out of touch with the world they live in today."