Jeremy Corbyn's rivals for the Labour leadership have complained about the election process, as the party revealed over 600,000 people had applied for the right to vote in the contest.
Andy Burnham, Yvette Cooper and Liz Kendall have written to the Labour Party to complain that they will only get an accurate list of who is eligible to vote in 10 days time even though voting starts on Friday. "It would appear unreasonable for an election to be taking place without the provision of a full list of voters," the three campaigns write.
The three candidates are worried that the the contact details of the "affiliated supporters" - largely union members - will be withheld from them but could made available to Corbyn directly by the unions themselves.
However Corbyn's campaign said this was not true. A spokesperson said: "As it has been reported that affiliated supporters' data is likely to be made available to campaigns with respective union support, from Jeremy's campaign we wish to be clear: this is, simply, factually inaccurate - all campaigns get the same data at the same time."
In the letter, published in full on LabourList, they write: "We believe it is essential that campaign teams have maximum ability to contact potential voters, especially as the affiliated supporters data is likely to be made available to candidates who have the respective union support. This would not be a level playing field for all candidates."
Labour revealed this evening that in total 610,753 people applied to vote in its leadership election, with around 400,000 people having signed up since the election.
The party indicated some may still be denied a vote if they are found to be Labour opponents trying to unfairly tip the contest in one candidate's favour.
On Wednesday, Labour MP Simon Danczuk said Corbyn would face a coup against him by his MPs on the first day after he was elected leader.
Corbyn, the veteran leftwinger, has become the surprise frontrunner in the race to succeed Ed Miliband - much to the horror of those in the centre and on the right of the party.
Danczuk, who has called on the contest to be halted, said Corbyn would not last in office for "about 12 months". Asked on LBC radio if the plotting would begin on "day one", he said: "Yeah, if not before. As soon as the result comes out. People in the PLP [Parliamentary Labour Party] aren't going to put up with it. "
The Rochdale MP, who was also a harsh critic of Ed Miliband, said he would not put up with the "crazy leftwing policies" advocated by Corbyn.
Labour had to extend the deadline for people to register to vote in the leadership contest from midday until 3pm today after its website crashed. Ballot papers will be sent out on Friday and the result will be announced on September 12.
Commenting at the end of registration to participate in the leadership election, Corbyn said today: "The response to the Labour leadership race from party members and supporters, longstanding and new, is proof of the optimism in the possibility of a popular, modern alternative to the Conservative government.
"All of our focus must be on channelling this extraordinary movement towards a united party that is able to find its confidence and defeat the Conservatives in 2020.
"I particularly want to pay tribute to the Labour Party’s staff who have worked so hard to deliver a robust selection system in totally new circumstances. The professionalism and commitment of the party’s staff shows our movement at its best."
The party has seen a surge in the number of people able to vote in its leadership contest since the election.
Some 282,000 party members, 92,000 trade union and other affiliated members are eligible to vote, but members of the general public can cast a ballot by joining Labour as a "registered supporter" for £3, with 70,000 so far signing up.
However some in the party are worried that it is being infiltrated by the hard left who are actually opposed to Labour values.
Around 1,200 members or supporters of another party have already been excluded from voting in the leadership contest, including hundreds who stood against Labour in local or national elections.
They included 214 from the Green Party, 37 from the Trade Unionist and Socialist Coalition, 13 Tories, seven from Ukip and one from the BNP.
Jeremy Corbyn's London rally
On Tuesday a YouGov poll for The Times showed Corbyn now has a staggering 32-point lead over Andy Burnham, his nearest rival.
The left-wing candidate is poised to win in the first round of voting having polled 53 per cent of the vote - a 10 per cent surge on a month ago. Corbyn, who wants Trident scrapped and industries re-nationalised, has pulled well ahead of Burnham on 21 per cent, Yvette Cooper on 18 per cent of the vote, and Liz Kendall with just eight per cent.
YouGov President Peter Kellner has said he would be "astonished" if Corbyn did not win the leadership race but added: "I have seldom released a poll with as much trepidation as I have done this time."
Labour figures from the centre and right of the party have issued repeated warnings that Corbyn will not be able to win a general election.
Alastair Campbell, Tony Blair's former communications director, said a Corbyn victory in the leadership race would lead to "chaos". In a blog post this week he urged Labour members to choose "Anyone but Corbyn" and encouraged people to sign up as a registered supporter for £3.