Labour leadership contender Liz Kendall has hit back at claims that the party is too "challenging" for either of the two women in the contest to cope with.
Ms Kendall said the comments by shadow justice secretary Lord Falconer of Thoroton were a "gross insult".
The peer, a former flatmate of Tony Blair, said that while Ms Kendall and Yvette Cooper were both talented politicians, neither was likely to be able to see off the hard left challenge of Jeremy Corbyn.
The comments drew an angry response from Ms Kendall who accused Lord Falconer – who is backing Andy Burnham for the leadership – of showing a lack of respect for the contribution women had made to the party.
"It is depressing to see a senior man in the party dismiss the contribution of women so easily," she said.
"Charlie made a great contribution to the last Labour government and I would have thought he would have learned that one of the reasons we achieved so much was because there was a record number of women around the top table.
"For Charlie to say that women somehow aren't tough enough to lead the Labour Party is a gross insult and, as for standing up to Jeremy Corbyn, I'm the only candidate who has been saying he would be a disaster for our party and that I wouldn't serve in his shadow cabinet, unlike the candidate Charlie is supporting."
Ms Kendall, seen as the favourite of the Blairites, has already had to fend off calls to drop out to give either Mr Burnham or Ms Cooper a clear run against Mr Corbyn after a shock opinion poll suggested he was on course to win.
Writing on The Times website, Lord Falconer said of Ms Kendall and Ms Cooper: "Both have a big future in our party. But neither Yvette nor Liz can steer the Labour party through the challenging few years ahead of us when we need a leader who can reach out to all wings of our party and provide unity.
"As a result, both Liz and Yvette are unlikely to beat Jeremy."