More than 100,000 people have joined Labour in recent weeks as the party prepares to elect a new leader to replace Jeremy Corbyn following its disastrous election defeat.

The surge was revealed to HuffPost UK by a senior party insider and will fuel suggestions that an influx of so-called moderates could harm the leadership prospects of Rebecca Long-Bailey, who is seen as the candidate to carry the Corbynite left’s torch.

Local constituency Labour parties (CLPs) are said to have been reporting rises in membership of up to 20% with the deadline to sign up as a member to vote in the leadership contest looming at 5pm Monday.

It comes after party grandees including Alastair Campbell, Tony Blair’s former spin doctor, urged people to sign up to end the left’s grip on the party following its catastrophic December election defeat.

The influx of new members, who pay £4.30 a month, does not include the 14,700 who have paid £25 to become registered supporters who can vote in the leadership election.

The surge will also provide a timely boost to Labour’s cash-strapped coffers following the election defeat, when the party had around 500,000 members.

Jess Phillips, one of the leadership contenders who might gain from a boost in moderate members, said the surge was “great to see”.

Earlier, Phillips insisted she was not an “uber Remainer” after making headlines earlier this month by refusing to rule out campaigning to rejoin the EU.

But she told Sophy Ridge on Sunday on Sky News: “I don’t think this is a conversation that’s even up for debate at the moment.

“There’s no plan to have some sort of campaign to rejoin the European Union.

“But any prime minister who wouldn’t look at the merits of every single alliance that our country could have for our safety, security, peace, and economic viability with a reasoned head on, anyone who closes off any option in the future, I just believe that that’s an honest position.”

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Meanwhile as the leadership candidates seek the nominations of unions and CLPs in order to make it to the next stage of the contest, Aslef general secretary Mick Whelan said his union would be meeting contenders over the coming days before deciding who to support.

Whelan told Sky News: “We need to articulate that voice of ordinary people that the Conservative party seem to have claimed in the short-term because of a one-topic process.

“The real message is about the four million people that are in poverty, 1.5m people in destitution, those who are in non-work, faux self-employment or zero-hours contracts, we need to give those people a voice.”

The latest YouGov Labour members poll for the Times showed frontrunner Sir Keir Starmer increasing his lead over Long-Bailey.

Starmer was predicted to win in the final round by 63% to Long-Bailey’s 37% if the contest took place on Friday, when the poll was published.