Former Czech secret agent Jan Sarkocy - also known as Jan Dymic - said he met the Labour leader in the 1980s and paid him money for information.
He said Corbyn's information was "rated in Moscow as the number one".
The Sun front page is the latest in a series of allegations thrown at Corbyn since he became Labour leader, which intensified during last year's general election campaign.
The Labour spokesperson added: "As Svetlana Ptacnikova, Director of the Czech Security Forces Archive, has made clear, Jeremy was neither an agent, asset, informer nor collaborator with Czechoslovak intelligence".
'The former Czechoslovak agent Jan Sarkocy's account of his meeting with Jeremy was false 30 years ago, is false now and has no credibility whatsoever.
The story, based on "secret files", alleges "he [Corbyn] passed on material about the arrest of an East German and was allegedly put on a list of Czechoslovakian state security team's agents and sources".
Mr Corbyn said he thinks goalkeepers have the most hard job on the football pitch, as he described former Arsenal stopper Jens Lehmann as a "very interesting guy". Did he, as reported, warn him of a crackdown by British intelligence? They were the enemies of the West.
They were told to break all links with other Communists and use their talents and educational success to penetrate the corridors of power.
"When the Sunday Times falsely accused Michael Foot of being a Soviet "agent of influence" he sued, won, and bought a new kitchen", said Paul Richards, who served as a special adviser to Hazel Blears and Patricia Hewitt.
Sir Richard also suggested the spies from Czechoslovakia were being used as a front by the Russian KGB.
They added: "Like other MPs, Jeremy has met diplomats from many countries".
In an interview with the COPA90 YouTube channel, posted on the Guardian website, Mr Corbyn said: "I would love to say England but I doubt it. Brazil or Germany".
Williamson said: "Time and time again he has sided with those who want to destroy everything that is great about this country, whether it is sympathising with terrorists, backing rogue regimes, or cosying up to those who want to inflict pain and misery on the British people". "He can not be trusted".
Experts called on the Labour leader to officially ask for his file and reveal its contents.