Jeremy Corbyn has surged to a 20 point lead over his rivals in the Labour leadership race as Yvette Cooper jumped into second place in the contest, according to private polling.
The survey, which was seen by The Daily Mirror, put the left-wing firebrand on 42%, Cooper on 22.6%, Andy Burnham on 20% and Liz Kendall trailing with 14% on first preference votes.
But Corbyn's lead is dramatically diminished when second preference votes are taken into consideration. The data puts the Islington North MP on 51% against Cooper's 49%.
The figures come after an independent poll from YouGov, which was commissioned by The Times, estimated that the socialist leadership contender had a 17 point lead over Burnham (43% vs 26%) on first preference votes.
The Mirror data is in line with other polls by predicting that Corbyn is in first place, but the significant difference is that the survey has placed Cooper second.
This means anti-Corbyn supporters could be drawn to the former work and pensions secretary as the most statistically viable "anything but Corbyn" candidate, rather than bookies' favourite Burnham.
The latest poll comes after claims of left-wing entryism into the party thanks to Labour's £3 "supporters" fee offer, which enables people to vote in the contest without becoming a member of the party.
But a source on the Socialist Party's (England and Wales) national committee told IBTimes UK that the group, formerly known as the Militant Tendency, was not practising entryism.
Instead, the Trotskyist organisation plans to open talks with Corbyn if he loses the leadership contest in a bid to break up Labour.
Ed Miliband's successor will be announced on 12 September at a special Labour conference and ballot papers for the vote will be set out on 14 August.
Kendall's, Burnham's and Cooper's campaign had not responded to a request for comment at the time of publication.