The Labour Party leadership contest has been a "disaster", former home secretary Charles Clarke has said.
Clarke told BBC Newsnight on Monday evening that the new election rules, which allow people to pay just £3 to vote for the leader, were a "mistake".
The former cabinet minister also revealed that he had voted for Liz Kendall in the contest. He gave his second prefernce to Yvette Cooper and his third preference to Andy Burnham. He did not vote for Jeremy Corbyn.
"I think it’s been a disaster actually, I’m very sad about it," he said. "We’ve got legal challenges, I think there may still be further legal challenges about the process, issues about who can vote who can’t vote, many party members who have been active for years distressed to see people who have been campaigning against the party with an equal vote to them in these circumstances, and I think we’ve made a series of mistakes."
Asked who was to blame for the trouble in the contest, he said: "I think the NEC, I don’t think Harriet’s done very well, I think the changes Ed Miliband brought in were a mistake and many people argued that at the time, and there have been a series of mistakes of this kind."
Harriet Harman will seek to reassure the Labour leadership candidates they face a fair contest amid claims of mass infiltration by political opponents.
The interim leader has invited the four rivals for talks on Tuesday to address warnings inadequate vetting would leave the result of the race open to legal challenge.
The contest has been marred by claims of "entryism" by Conservatives and others paying £3 to become registered Labour supporters under the new party rules.
There have also been complaints about legitimate voters - many of them supporters of surprise front-runner Jeremy Corbyn - being unfairly blocked.
In a fresh sign of the level of concern felt by senior party figures about the growing prospects of a win for Corbyn on September 12, Gordon Brown publicly backed Cooper.
The former prime minister's office announced that he had given his second-preference vote to Burnham and his third to Kendall, a clearly calculated snub to the veteran left-winger.