Agents of the security services may be responsible for the bullying and abuse of critics of Jeremy Corbyn in an attempt to stir up trouble for the Labour leader, the Unite trade union boss Len McCluskey has claimed.

Mr McCluskey, a strong supporter Mr Corbyn, said the security services had a history of "dark practices" and suggested "right-wingers" in disguise may be responsible for the actions attributed to the Labour leader's supporters.

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"Do people believe for one second that the security forces are not involved in dark practices?" he told The Guardian.

"We found out just a couple of years ago that the chair of my union then, the Transport and General Workers Union, was an MI5 informant at the time that there was a strike taking place that I personally as a worker was involved in.

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"(In) 1972, I was on strike for six weeks. And 30 years later it comes out that the chair of my union at that time was an MI5 informant."

"Anybody who thinks that that isn't happening doesn't live in the same world that I live in. Do you think that there's not all kinds of right-wingers who are not secretly able to disguise themselves and stir up trouble? I find it amazing if people think that isn't happening."

Mr McCluskey accused MPs and others in the party who had complained of death threats and intimidation of exaggerating the problem.

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"There's a hysteria being whipped up. A few people say things they shouldn't and then it's blown up out of all proportion, to suit the imagery that the Labour party has somehow become a cesspit, and suddenly it's a crisis," he said.