The deadline to secure a vote in the Labour leadership contest will be passed at 5pm on Wednesday, with celebrities including author JK Rowling urging moderates to pay £25 in the hope of removing Jeremy Corbyn.

But Mr Corbyn too was making a last-minute drive to get his backers to sign up, and thousands of new supporters are expected to rush to register for a vote in the last hours before the electorate is finalised.

The Labour leader is facing a challenge from former shadow work and pensions secretary Owen Smith in an all-male contest, after Angela Eagle withdrew her candidacy on Tuesday.

Ms Eagle has offered her support to Mr Smith, who says he will make her his "right-hand woman" if he wins the postal vote of Labour members and affiliated and registered supporters, which ends on September 24.

A trade union is considering legal action over the decision by the party's ruling National Executive Committee barring an estimated 130,000 new members who joined after January 12 from voting.

The only way for them to get a vote now is to pay £25 to become a registered supporter before the 5pm Wednesday deadline.

Manuel Cortes, general secretary of the Transport Salaried Staffs' Association, which has almost 1,000 members affected by the cut-off date, said Labour "appears to be happy to take their hard-earned cash but appears to be hell-bent on denying them a voice".

Seeking legal redress was "the least we can do to overturn an unjust ban on ordinary working people", he said.

Meanwhile, the Saving Labour campaign urged those opposed to Mr Corbyn's leadership to sign up as registered supporters, saying: "Britain and Labour needs new, strong leadership for the months ahead."

Harry Potter author JK Rowling backed the campaign, saying it was "for those who feel we need a decent opposition", while Emmerdale actor Nick Miles said: "It's time for Corbyn to resign for the good of our country."

There were signs that Corbyn's campaign may seek to target Mr Smith's past as a lobbyist for US drug company Pfizer, when he was quoted as speaking out in favour of choice in healthcare.

The Times quoted an unnamed "senior Corbyn ally" as saying: "Bring on the Blair-lite candidate. Our members won't be fooled by a TV-savvy turncoat who lobbied big pharma and Tony Blair."

In a statement on the Labour website, Mr Corbyn acknowledged the party was "divided", but added: "We need to use this contest to bring people together around strong policies to turn our fire onto the Tory government."

He said he would fight for "an economy that delivers for everyone, in every part of the country" and urged those involved in the campaign to avoid personal abuse or threatening behaviour and ensure it was a "comradely debate".

Pontypridd MP Mr Smith, who secured the nominations of 88 of Labour's 230 MPs as well as two MEPs to win his place on the ballot paper, said he would "unite Labour with a radical vision for the future of our party and Britain, backed up by a credible plan to deliver".

Labour MP Jess Phillips, who backed Ms Eagle, said she was "disappointed" there would be no female candidate but was now switching her support to Mr Smith.

The Birmingham Yardley MP told Channel 4 News she would find it "incredibly difficult" to continue as a Labour MP if Mr Corbyn won, but declined to say whether she would sit as an independent.

Asked how Labour MPs would respond if Mr Corbyn won - as polls suggest he will - Smith backer Stephen Kinnock told BBC2's Newsnight: "Those of us who have given a motion of no confidence will be honoured to serve our constituents from the backbenches, and it will be up to the leader to figure out how he forms a credible and effective opposition. I see it as a very difficult challenge for him to face."

But James Schneider, of the Corbyn-backing Momentum group, told Newsnight: "Everybody should accept the result. We've got a democratic election and then whoever wins, we should get behind whoever is supported and move forward as a party."

Mr Smith said he had had his arm twisted in the decision to run against Mr Corbyn, whom he had previously supported.

He said he had received more than 30 phone calls from colleagues urging him to stand in the contest.

Mr Smith, who is Mr Corbyn's sole opposition after Ms Eagle's decision to pull out of the race, said he had spoken with his leader and asked him to change tack, but he was "completely intransigent" and would not step aside.

He told ITV's Good Morning Britain people are worried "that under his (Mr Corbyn's) watch the Labour Party will split, so great are the divisions growing that we face the prospect of the Labour Party, that's been the greatest vehicle for social good in Britain for 100 years, splitting apart and being destroyed".

He added: "I am standing to heal the Labour Party, to unite us, to get us around a radical programme, to say to the country once more not just that we can be a strong opposition to a Tory Government that is frankly making life rotten for many people, but we can be a government in waiting."

Asked if he would authorise the use of nuclear weapons if he became prime minister, Mr Smith said: "Yes is the unfortunate answer to that because, if you are serious about defence and serious about having a nuclear deterrent, then you have to be prepared to do that."

Questioned by presenter Piers Morgan about an incident in his past when he called a police hotline for a comment on a story while working at the BBC, Mr Smith admitted he was embarrassed and had made a mistake.

He said: "There was a bit of a, to be honest, a culture of bullying."

He added: "It was very embarrassing with colleagues at the time, and it was very embarrassing when the police did make a complaint about it."