A former Labour activist spied for the Czech government when it was controlled by the Soviet Union, it has been claimed.
Left-winger Cynthia Roberts, who once stood as a parliamentary candidate for the party, worked for the communists under the codename Operation Hammer, according to the Mail on Sunday.
Czech security service documents obtained by the paper show she prepared files on Tory politicians, including Margaret Thatcher, after moving to Prague in 1985.
She also allegedly provided details of a British arms factory.
Before moving to the Czech capital Ms Roberts was involved with the Labour Action for Peace (LAP) group, which was widely held to have links with the Soviets at the time.
Robin Cook, who decades later went on to serve as Foreign Secretary in Tony Blair's first administration, was involved with the group during the same period. LAP is still in existence, and chaired by Labour MP Jeremy Corbyn.
The files held by the Czech secret service reportedly state that Ms Roberts' role was to "contribute towards the downfall of capitalism".
She is also said to have prepared a file on the then-Foreign Office minister David Mellor in 1988, in which she said it was not known if he had "any weakness for women".
Her handlers may have questioned her usefulness when four years later Mr Mellor was embroiled in an explosive sex scandal, involving lurid claims that he made love to Antonia de Sancha in a Chelsea FC strip. He subsequently resigned from John Major's government.
Challenged by the MoS in Prague this week, 72-year-old Ms Roberts replied: "I have nothing to say. I was not a spy."
