A left-wing MP who entered the race for the leadership of Britain's opposition Labour party as a wildcard may be on course to win with a commanding lead, according to the latest poll.

Support for Jeremy Corbyn, 66, a veteran socialist and anti-nuclear campaigner, has increased to give him the backing of over half of those eligible to vote in the contest, according to the poll by YouGov.

"I would personally be astonished if Corbyn does not end up as Labour's leader," wrote YouGov president Peter Kellner, while acknowledging the race could change before voting ends in a month's time.

The poll of 1,411 eligible voters showed Mr Corbyn with 53 per cent support, far ahead of his nearest rival, Andy Burnham on 21 per cent.

According to the poll, Mr Corbyn's support is stronger among those who joined the party after Labour was resoundingly beaten by the Conservatives in May's general election.

Seen as the most left-wing of the four candidates, Mr Corbyn's increasing popularity comes despite a series of stark warnings from senior Labour figures that he could damage the party's chances of beating the Conservatives in future elections.

His rivals, who include two former cabinet ministers, say the perception that Labour was anti-business was one of the reasons it lost the May election.

Former Labour prime minister Tony Blair warned it would be impossible to win an election from a "traditional leftist platform", while his ex-communications chief Alastair Campbell said a victory for Mr Corbyn would be a "car crash" and urged supporters to vote for "anyone but Corbyn".

Mr Corbyn wants to return the centre-left party to its socialist roots and has filled speaking venues across England with his platform of restoring public control of railways and utilities and ending austerity.

Starting the contest as a rank outsider who barely managed to get his name on the ballot, bookmakers are now ranking Mr Corbyn as their frontrunner.

The results of Labour's internal vote will be announced on September 12 at a special conference.

AFP/Reuters