Ex-Labour Foreign Secretary Margaret Beckett has described herself as a "moron" for nominating Jeremy Corbyn for the Labour leadership contest.
"At no point did I intend to vote for Jeremy myself - nice as he is - nor advise anyone else to do it," she said.
"We were being urged as MPs to have a field of candidates," she told the BBC.
Ex-adviser to Tony Blair John McTernan had said MPs who "lent" their nominations to Mr Corbyn to "broaden the debate" were "morons".
He made his comment on the BBC's Newsnight on Tuesday.
During an interview with BBC Radio 4's World at One Mrs Beckett was asked if she was, as Mr McTernan put it, a moron for nominating Mr Corbyn. She replied: "I am one of them."
Mrs Beckett, who held a series of top positions in the party including being acting leader, is supporting Andy Burnham in the current Labour leadership contest.
There are four candidates for Labour leader - Yvette Cooper and Liz Kendall are the other two. The result will be declared on 12 September.
'Field of candidates'
Mrs Beckett said she had believed there should be a wider debate about austerity and the future direction of the party, but was beginning to regret her decision with Mr Corbyn topping a YouGov poll in The Times.
"To a certain extent to be honest, yes I do," she said. "We were being urged as MPs to ensure that the party had a field of candidates and that I thought was a perfectly legitimate point of view.
"If Jeremy had been a long way behind, I don't think the thought of nominating him would have crossed my mind. But then when it looked as if he might almost be able to stand but then not be able to, I was concerned that people would feel that they had been deprived of the opportunity for their point of view to be aired.
"But yes, I'm beginning to wish that I hadn't, to be quite honest about it."
Mr Corbyn secured 36 nominations, one more than was needed to qualify for the contest. As many as 12 of the MPs who nominated him actually support other candidates but lent him their support to get him on the ballot paper.
Richard Burgon, the MP for Leeds East who has supported Mr Corbyn throughout the contest, said he did not regret doing so and said to characterise some of Mr Corbyn's last-minute backers as morons was "unfortunate and unfair".
"I don't regret nominating Jeremy Corbyn and I certainly don't regret campaigning alongside him now and taking part in a campaign that's enthused tens of thousands of Labour party members and supporters across the country," he said.
Speaking on Wednesday, Mr Corbyn said his campaign was going well but talk of him winning was "premature".