SCOTTISH Nationalists have infiltrated the Labour leadership campaign, it has been claimed, as calls were made for acting leader Harriet Harman to halt the contest until checks on bogus supporters could be made.

A senior Labour insider said: “There is definitely entryism going on; the question is whether or not it is on an industrial scale.”

The source claimed there had been a “direct appeal” by the Jeremy Corbyn camp to SNP supporters to sign up as Labour backers to influence the race in favour of the leftwinger. Asked if some had done so, he replied: “Yes, I believe so.”

Scottish Labour’s Neil Findlay, chairman of Mr Corbyn’s Scottish campaign, has previously urged leftwingers opposed to austerity and nuclear arms to “put aside differences for a short period” to become a registered supporter for £3 to enable them to participate in the leadership contest.

But the MSP denied he was actively encouraging diehard Nationalists to take part in choosing Ed Miliband’s successor; rather, he stressed, he was attempting to get traditional Labour voters in Scotland, who were anti-austerity and anti-Trident and who had abandoned the party at the General Election, to return to the Labour fold.

“Now in the leadership race, we have a candidate who is clearly anti-austerity, who has campaigned for peace and has been opposed to nuclear weapons all his life. This is a great opportunity for the Labour Party to bring back some of those people to our cause and we have to bring them back, if we are going to win elections again,” added Mr Findlay.

An SNP spokesman commented: “Labour’s leadership election is entirely a matter for them but, with the SNP providing the only real opposition to the Tories in Westminster, the reality is that more and more former Labour supporters are turning to the SNP. “

Earlier, Alex Salmond, the former party leader, made clear it would be possible for the SNP to “co-operate” with a Corbyn-led Labour Party on key issues like opposing austerity and nuclear weapons.

While the MP for Gordon stressed he did not agree with the London MP on everything, he described him as a substantial politician and denounced the “demonization” of him by the Metropolitan Press.

It has been estimated since the election up to 140,000 people have joined, registered, or associated to Labour, enabling them to vote in the leadership contest.

Labour backbencher John Mann warned the situation was "totally out of control" and demanded the contest be halted.

However, Andy Burnham, the Shadow Health Secretary, who had been the favourite until shock polls put Mr Corbyn ahead by a sizeable margin, branded demands for a pause "unhelpful".

"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."

Mr Corbyn, meantime, stressed he only wanted genuine Labour supporters to participate but also appeared unconcerned, saying the growth in the Labour roster was mainly due to “lots of young people who were hitherto not very excited by politics coming in for the first time".

Commenting on the plight of Scottish Labour, Mr Corbyn said it was "way out of touch with the general ambit of a lot of Scottish public opinion on Trident, on austerity, on housing, on welfare issues”.

He added: “Labour in Scotland is going to grow again; it will rediscover again essentially what its roots are".