Labour leadership frontrunner Jeremy Corbyn has dodged questions about whether he is a Marxist as he dismissed warnings that the contest is being warped by hard-left "infiltrators".
The Islington North MP said an influx of up to 140,000 activists was mainly "young people" who were enthused by his brand of politics.
The comments came after two backbenchers called for acting leader Harriet Harman to halt the race while checks were carried out on newcomers.
John Mann told the Sunday Times the situation was "totally out of control".
"It should be halted," the Bassetlaw MP said. "It is becoming a farce with long-standing members ... in danger of getting trumped by people who have opposed the Labour Party and want to break it up, expressly want to break it up - some of it is the militant tendency types coming back in."
Blackley and Broughton MP Graham Stringer said in an interview on BBC Radio 4's World This Weekend that Tories were also trying to influence the outcome.
"I am worried that people who do not have the interests of the Labour Party at heart are joining the Labour Party," he said.
"It is not that I am particularly concerned whether Jeremy or Yvette or anybody else is elected. Whoever is elected I want them to be chosen by Labour Party members."
However, shadow health secretary Andy Burnham, who had been the favourite until shock polls put Mr Corbyn ahead by a sizeable margin, branded demands for a pause "unhelpful".
Mr Burnham told Sky News' Murnaghan programme. "I'm comfortable with people joining the Labour Party. 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."
Frontbencher Caroline Flint, a candidate for the deputy leadership, said she had not seen anything to worry about.
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."
The number of full Labour members is expected to be 66,000 higher than on May 8 by the cut-off point of August 12.
Another 22,000 people are likely to take advantage of new rules introduced by Ed Miliband that allow them to pay £3 to become "registered supporters". Only around 30 applications for that category are believed to have been rejected, most from Tories.
Some 55,000 extra "affiliate" members are also being signed up by unions.
Mr Corbyn said the growth in the Labour roster was mainly due to enthusiastic "young people".
"The entryism that I see is lots of young people who were hitherto not very excited by politics coming in for the first time," he told the BBC's Andrew Marr show.
"I have said all along from the very beginning I only want people to register as Labour supporters if they are genuinely Labour supporters and they want to stay. Personally I would prefer it if all those supporters became party members."
Mr Corbyn reiterated his desire to renationalise the railways and utilities, arguing that Labour lost the election because it was "too close to the economic orthodoxy".
"It has been too close to big business, it has been too close to economic orthodoxy," he said.
Asked whether he thought debt was a problem for Britain, he replied: "The austerity process makes it worse because it lowers income, lowers wages, lowers income tax, increases demand on welfare because of the levels of poverty in Britain.
"So it actually is a cycle of decline. Surely it is better to invest in an economy, to grow income and grow prosperity."
Pressed directly on whether he was a "Marxist", Mr Corbyn said: "That is a very interesting question actually. I haven't thought about that for a long time. I haven't really read as much of Marx as we should have done. I have read quite a bit but not that much."
He said: "I think Marx's transition of history and the analysis of how you go from feudalism to capitalism and move on to a different stage is fascinating."
"Marx obviously analysed what was happening in a quite brilliant way. The philosophy around Marx is absolutely fascinating," he said.
"Does it all apply now? Well obviously philosophy applies at all times. Do we then take that as a way in which we ensure that people have reasonable security in their lives through public ownership of the major monopolies? I think that is a fair point to look at. It is not unpopular with the public."
Mr Corbyn went on: "I am not talking about the Labour Party being a revolutionary party. It certainly isn't. What we are doing here is putting forward a view that the Labour Party has to offer a credible alternative that is true to the roots of the Labour Party, the roots of the Labour Party are essentially democratic, essentially socialist, essentially community."
Labour backbencher Simon Danczuk said victory for Mr Corbyn was a realistic prospect but would be "a nightmare".
But he insisted the party could not halt the contest and the other candidates had to focus on beating the left-winger.
"I don't think we can (pause the contest), to be honest. I think we are where we are," he told the Press Association. "The party is in a terrible place.
"It is quite clear there has been some movement to try and get people who are Conservatives to sign up to be supporters."
A Labour Party spokeswoman said: "While we want the widest number of supporters to have their say in Labour's leadership contest, the Labour Party has a robust system to prevent fraudulent or malicious applications.
"All applications are verified against the Electoral Register, and any who are identified by our verification team or by local Labour branches as not sharing the aims or values of the Labour Party will be denied a vote."
Blairite candidate Liz Kendall told the Independent on Sunday Mr Corbyn's politics were "not right for Labour or the country".
Meanwhile, shadow home secretary Yvette Cooper warned in the Sunday Mirror: "Get this wrong and we will write off the 2020 election and condemn Britain to a Tory future."
Former cabinet minister Alan Milburn told Murnaghan Labour risked being cast into "political oblivion".
Mr Corbyn was a "perfectly nice chap" but "not even Jeremy thinks he is prime ministerial material".
Ex-SNP leader Alex Salmond said he could work with Labour on "a range of issues", such as welfare reform and abolishing Trident, if Mr Corbyn became leader.