Jeremy Corbyn has categorically denied claims that he acted as an informant for an Eastern Bloc spy during the Cold War.
The Labour leader dismissed suggestions that he passed information to an agent of the Czech StB intelligence agency during the 1980s as “nonsense” .
Reports that appeared in The Sun have been dismissed by Labour as having been borrowed from “the plot of a bad James Bond movie”.
Mr Corbyn was challenged about the allegations by a journalist from the Daily Mail during a question and answer session at the EEF manufacturers’ conference in London, where he had delivered the keynote speech.
He replied: “I am sorry the Daily Mail has reduced itself to reproducing some nonsense that was written in The Sun.”
Asked directly by BBC Breakfast presenter Steph McGovern, who was acting as compere for the event, if he had been a “Czech spy”, he said, “No”.
Documents unearthed in the StB archives claim Mr Corbyn met Czech agent Jan Sarkocy, who posed as a diplomat at the Czechoslovak embassy, on at least three occasions in 1986 and 1987, including twice in the House of Commons, and was given the codename Cob.
However, Mr Corbyn has said he can only recall one meeting with Mr Sarkocy, and as a Labour backbencher with Irish republican sympathies he would not have had any state secrets to offer.
His denial came after Tory MP Ben Bradley was threatened with legal action over a tweet claiming he “sold British secrets to Communist spies”.
Mr Bradley’s tweet was removed after a Labour spokesman said Mr Corbyn had “instructed solicitors to contact Ben Bradley to delete his libellous tweet or face legal action”.
The Labour leader’s office acknowledged that he had had tea in the Commons with a Czech diplomat but said any claim that he was “an agent, asset or informer for any intelligence agency is entirely false and a ridiculous smear”.
The Czech agent was expelled from the UK in 1989 in a tit-for-tat row over spying. In interviews, Mr Sarkocy suggested that as many as 15 senior Labour figures were paid for information, although he retracted an earlier claim that Mr Corbyn had sold state secrets.
Insisting that Mr Corbyn had been part of a “conscious cooperation” to pass information to the StB, Mr Sarkocy said: “Everybody knew that ‘diplomat’ was just a cover for spy. It was a conscious cooperation. Diplomat and agent were the same thing...
“He was our asset. He had been recruited. He was getting money from us.”
Michal Miklovic of the Slovak National Memory Institute, which has access to secret police records, claimed Mr Sarkocy would have tried to uncover information about British intelligence. He told the Times: “The most important task of Jan Sarkocy in Britain was to get the information about British secret services. It’s possible he assumed that Jeremy Corbyn, as MP, may obtain this kind of information.”
However, experts in the Czech Republic suggested Mr Corbyn had not provided any information. Svetlana Ptacnikova, the director of the Czech security service archive, said: “Mr Corbyn was not a secret collaborator working for the Czechoslovakian intelligence service.
“The files we have on him are kept in a folder with the identification number one. Secret collaborators were allocated with folders that started with the number four.
“If he had been successfully recruited as an informant, then his person of interest file would have been closed and a new folder would have been opened.”
Mr Corbyn has also come under pressure to give permission for any files held on him in the archives of the East German secret police, the Stasi, to be published.
A Labour source said the party had no knowledge of any Stasi files.