Shadow chancellor John McDonnell has denied meeting any Czech spies.
He said claims that he had been a KGB agent dated back to when he was a council officer in Camden.
Speaking in central London, he told a think tank: “I promise you, I was not selling secrets to the KGB”, about the north London council’s policy on housing.
Mr McDonnell was asked during a question-and-answer session at the Resolution Foundation if he had ever met agents from the former Communist state.
He said: “No, I have not met any Czech spies, et cetera.”
It comes after days of headlines about Jeremy Corbyn’s activities during the Cold War.
The Labour leader has dismissed claims that he passed information to an agent of the Czech StB intelligence agency during the 1980s as “nonsense”.
According to the original report in the Sun, documents unearthed in the StB archives showed that Mr Corbyn met a Czech agent on at least three occasions – including twice in the House of Commons – during the 1980s and was given the codename Cob.
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”.
Mr McDonnell joked that he went into a shadow Cabinet meeting and greeted colleagues by saying “Zdravstvuyte tovarishchi”, which means “Good day, comrades”.
“I said ‘You haven’t read the papers this morning, have you?’,” he added.