Andy Burnham was accused of “swerving all over the place” by rival Yvette Cooper after he offered a post to frontrunner Jeremy Corbyn.
A day after he was quoted as saying that he would put Mr Corbyn in his shadow cabinet, Mr Burnham appeared to downgrade the offer.
Speaking in Manchester, the shadow health secretary offered the olive branch by saying: “Jeremy has brought real energy to this race. I want to capture that and would involve Jeremy in my team from the outset.
“I want the people who are drawn to his campaign — particularly young people — to help us rebuild our party from the bottom up, to re-energise it, make it the people’s party again.”
But Ms Cooper accused him of courting disaster by tacking left and right to try to accommodate the surge of new members attracted by Mr Corbyn.
“We can’t move our narrow party a bit to the left or a bit to the right,” she told BBC radio. “But neither can we swerve all over the place because we will crash and we will lose in 2020. And then we let people down.”
The exchange came as the first of 600,000 Labour members, trade unionists and the new category of “registered supporters” began voting in the leadership contest. Polls suggest Mr Corbyn has a huge lead and could be unstoppable.
Mr Burnham struck a contrast with Ms Cooper and rival Liz Kendall by reaching out to Mr Corbyn. “There is a good deal of common ground between Jeremy and I on some of the big ideas he has brought to this race,” he said. He did not specify what role the Islington North MP would be given. Supporters of Mr Corbyn scoffed at the idea that the clear frontrunner would settle for a post without influence.
Ms Cooper denied knowing about a reported attempt by Lord Mandelson to suspend the election by persuading her, Mr Burnham and Ms Kendall to quit the contest.
The proposal was reportedly abandoned when officials made it clear that Mr Corbyn would win by default if the others quit.
