The Labour Party is preparing to elect its next leader after thousands of new members signed up to vote.

Candidates had urged supporters to sign up and the deadline, which has now passed, was extended after "technical issues" with the website.

Ballot papers will begin to be sent out on Friday, and the result announced at a special conference on 12 September.

There have been calls to pause the contest over fears the process is being sabotaged by members of other parties.

These have been dismissed by the party, which says efforts to weed out non-party supporters will continue up until results day.

Earlier left wing candidate Jeremy Corbyn tweeted that the system was "struggling with all the sign-ups", although this was not confirmed by the party.

Latest figures show almost 450,000 people are eligible to vote in the contest - party officials said 1,200 applications have so far been rejected as bogus.

Speaking on BBC Radio 2, backbench MP Graham Stringer, one of those calling for the contest to be halted over "infiltration" fears, said the election "has no credibility".

"I do not mind if Jeremy Corbyn is elected by the Labour Party," he said, adding that if Mr Corbyn was elected by party members, "that's democracy".

He added: "But if members of other parties elect him that is a conspiracy."

But another MP, Diane Abbott, told BBC News such calls were "silly", saying the party was "bending over backwards" to ensure no foul play.

Image copyright Twitter

Image copyright Twitter

On Twitter, Labour apologised that the site had been down, with some users replying to say they were still experiencing problems.

'Greatest disaster'

The popularity of Mr Corbyn's campaign has sparked warnings from his rival candidates and other senior party figures about a shift to the left.

Former Tony Blair adviser John McTernan told the BBC it would be "the greatest disaster in the history of the Labour Party" if the Islington North MP were to win.

In response, left wing journalist Owen Jones said: "If Jeremy Corbyn wins, he wins because he has an overwhelming decisive mandate from Labour Party membership."

Labour leadership contest

Image caption Labour leadership candidates (l-r): Yvette Cooper, Jeremy Corbyn, Liz Kendall, Andy Burnham

Who are the candidates? Andy Burnham, Yvette Cooper, Jeremy Corbyn, Liz Kendall

Andy Burnham, Yvette Cooper, Jeremy Corbyn, Liz Kendall Dates: Ballot papers will be sent out on 14 August; voting can take place by post or online. They must be returned by 10 September. The result is announced on 12 September

Ballot papers will be sent out on 14 August; voting can take place by post or online. They must be returned by 10 September. The result is announced on 12 September Who can vote? All party members, registered supporters and affiliated supporters - including those joining via a union

All party members, registered supporters and affiliated supporters - including those joining via a union What is the voting system? The Alternative Vote system is being used so voters are asked to rank candidates in order of preference

The Alternative Vote system is being used so voters are asked to rank candidates in order of preference How does it work? If no candidate gets 50% of all votes cast, the candidate in fourth place is eliminated. Their second preference votes are then redistributed among the remaining three. If there is still no winner, the third place candidate is eliminated with their second preferences (or third in the case of votes transferred from the fourth place candidates) redistributed. It is then a head-to-head between the last two candidates

At-a-glance profiles of the four contenders

The Labour Party has more than doubled in size since May's general election, with tens of thousands of people either becoming full members or registered supporters, driven to a large extent by a social media campaign by Corbyn supporters.

Labour says it now has 282,000 full members - an increase of more than 80,000 since the general election defeat.

A further 70,000 people have become registered supporters, meaning they are able to take part in the vote for a £3 fee if they agree they "support the aims and values of the Labour Party".

There are also 92,000 "affiliated supporters", largely trade union members.

Many of these people, including most of the affiliated supporters category, are "awaiting verification", Labour says.

The campaign teams of all four candidates attended a meeting on Tuesday designed to clear up confusion around how the contest would work.

Earlier Rochdale MP Simon Danczuk said he too believed the process may have to be rerun and warned that if Mr Corbyn wins he would not be able to command discipline amongst Labour MPs - many of whom would not vote for "crazy left-wing stuff".

Labour has dismissed such calls, and says it has a robust system in place to detect non-party supporters who are attempting to vote.