Leadership frontrunner dismisses calls from Labour MP John Mann for party to suspend election owing to fears of ‘infiltration’ by the hard-left

The frontrunner in the Labour leadership election, Jeremy Corbyn, has said he only wants the support of “genuine Labour supporters” as he sought to dismiss calls for the party to shelve the contest over fears of an “infiltration” by hard-left activists.

John Mann, the Labour MP for Bassetlaw, has written to the party’s interim leader, Harriet Harman, to call for the election to be suspended until proper checks can be carried out on the tens of thousands of new members who have joined Labour since its election defeat in May.

Mann told Harman: “[The election] should be halted. It is becoming a farce with longstanding members … in danger of getting trumped by people who have opposed the Labour party and want to break it up – some of it is the Militant Tendency-types coming back in.

“It is pretty clear that what is happening amounts to infiltration of the Labour party.”

Harman will reject the request for the race to be suspended, because the party already has processes in place to protect the integrity of its membership. Andy Burnham, one of Corbyn’s rivals for the leadership, said Mann’s allegations were unhelpful and challenged him to produce evidence to back up his claim.

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Speaking on the BBC1’s Andrew Marr Show on Sunday, Corbyn welcomed the influx of Labour members since the election and said: “What is there not to like about young people turning up and being interested in politics? What it’s about is converting Labour into much more of a social movement.”

He also addressed Mann’s fears directly, saying: “I only want people to register as Labour supporters if they are genuine Labour supporters and intend to stay for the longer course.

“Surely the idea of joining a political party just to vote in a leadership election is a bit limited and we should go a bit further. The entryism I see is a lot of young people hitherto not really excited by politics coming in for the first time and saying we can have a discussion – we can discuss our debts and housing problems.”

Corbyn suggested Labour’s full membership fee should be reduced so some of the registered supporters could join the party as full members.

Burnham said Mann’s allegations about so-called entryism were not helpful and he had no evidence of entryism on any scale. If Mann had any evidence, he should produce it, Burnham added.

“I’m comfortable with people joining the Labour party,” Burnham told Sky’s Murnaghan programme. “Of course there are processes in place to check if somebody is joining for the wrong reasons and the party has got long established procedures to deal with that, and I don’t have any evidence that that is happening on any wide scale.

“If John has evidence then he needs to send it to the Labour party, but we’re in the middle of a debate that is actually now finally capturing attention and I think that’s a good thing because I think the party needs to have this debate and then decide its future direction.

“What we need more than anything now is unity coming out of this contest. People might hear this call as an attempt by the establishment to kind of skew the race one way or another, I think we need to keep it positive. Let’s have the debate and then Labour needs to move forward together.”

Labour frontbencher Caroline Flint, a candidate for the deputy leadership, said she had not seen anything to cause concern. “We have had new members but nothing that causes me concern,” she told Murnaghan. “Look, what I would say is to anybody who feels there is evidence of people who for example are in parties that campaigned against us or who nominated candidates against Labour at the last general election, provide that evidence to Harriet Harman and the party so that they can scrutinise it.”

But there is concern among other Labour candidates about the kind of entryism last seen in the 1980s by the Trotskyist Militant Tendency, though they admit the scale of any infiltration is limited and does not explain Corbyn’s popularity, particularly among young people.

The deeper political fear of senior figures is that the wider reputation of the party is being damaged in the leadership process. Labour has allowed anyone to vote in the leadership election if they pay £3 and sign a form saying they share Labour values – which does not amount to a high barrier for involvement.

The reduced-fee right to vote was agreed at a special conference of the party as part of a new settlement in between the then Labour leader, Ed Miliband, and the unions in 2014. It was modelled on the French Socialist party elections to choose its candidate for president, but it appears that those joining for the reduced fee are heavily biased to the left, rather than the process broadening the Labour base to those less involved in party politics.

Since the election, the party has gained 60,000 new members, 22,000 registered supporters paying £3 and about 60,000 affiliated union supporters, many from the Unite union. A phone bank has been run by Unite to recruit its members to become affiliated supporters, and Labour is now supposed to be checking the names, including listening to some of the calls recruiting Unite members to affiliate with Labour.

Many members of the so-called ultra left have orientated their political work around the Trade Unionist and Socialist Coalition (TUSC), a separate political party that did badly in the election, but since then a small number of socialist groups, including a split from the Socialist Workers party, have argued that Labour’s election defeat changes the landscape.

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The Communist party, for instance, has urged its supporters to vote for Corbyn.

John Cryer, who chairs the parliamentary Labour party, told the Mail on Sunday that members of the TUSC have been joining as registered supporters, which gives them the right to vote in the leader and deputy leader elections.

The TUSC was formed in 2010 with the help of the Socialist party, the successor of Militant Tendency. Cryer told the newspaper: “These people were thrown out of the Labour party and should not be allowed to vote.”

The former minister Lord Hutton said it would be a “travesty” if members of Militant Tendency were able to influence the election.

Earlier this month, the Socialist party’s official newspaper backed Corbyn’s campaign, saying he would defend people “under the cosh” of welfare cuts.

It said the leadership contest rules were a “virtual lottery in which any individual, Labour supporter or not, can potentially vote. The result is a layer of people signing up in the leadership election in order to vote for Jeremy Corbyn”. The newspaper said if Corbyn won, he should lift Labour’s ban on Militant Tendency.

Labour has pledged to prevent abuse of the leadership vote. A party spokesman said: “We have a robust system to prevent fraudulent or malicious applications. All applications are verified against the electoral register, and any who are identified … as not sharing the aims or values of the Labour party will be denied a vote.”

However, fewer than 100 of the 17,000 new applications have been rejected as bogus.