Ken Livingstone, John McDonnell and Jeremy Corbyn were part of a group of at least 15 senior Labour figures who shared information with Eastern bloc agents, it is claimed.

Jan Sarkocy, a former Czechoslovak spy, described the MPs as “great sources” to himself or his colleagues in the KGB.

The new claims come after he said on Friday that the Labour leader had shared information with the Communist Czechoslovak regime.

Speaking to The Telegraph, Mr Sarkocy claimed that:

Mr Livingstone also discussed information with the Czechoslovak regime;

The future London mayor made frequent visits to the Czechoslovak embassy, where he drank whisky;

Mr McDonnell met a KGB agent on several occasions;

Between 10 and 15 Labour MPs held meetings with the Czechoslovak secret service.

Labour described the latest claims as “absurd”, while Mr Livingstone said they were a “tissue of lies”. He did admit meeting a Russian “representative” at the time, but said “nothing happened”.

The shadow chancellor dismissed the claims as “ridiculous”.

It is not known what information the politicians could have supplied.

The claims by Mr Sarkocy, who was revealed to have met Mr Corbyn three times in classified documents released by the Czech government, will place further pressure on the Labour leader over his attitude towards the Soviet bloc during the Cold War.