The son of a double agent is appealing to the British Government to force intelligence chiefs to reveal the files it holds on his father, as he believes his mother married him on the orders of MI5.
Francois Grosjean, emeritus professor of psycholinguistics at Neuchatel University, Switzerland, has been fighting a decade-long battle to find the truth about his parents.
Grosjean is convinced that he and his sister were the "unwanted consequences" of his mother being used to spy on his father, whose codename was Fido.
Roger Grosjean was a French fighter pilot who fled to Britain during World War II. When British intelligence discovered he had been approached by the Germans to steal a plane and fly it back to France, they recruited him as a double agent.
As with other spies after the war, Roger Grosjean went back into normal life, and obscurity. He died in Corsica in 1975.
It was not until almost 30 years later, when his stepmother gave him a box of old papers, that Grosjean started to learn of his father's work for British intelligence.
The Home Office said: "It is a longstanding policy neither to confirm nor deny whether an individual was ever an agent."
Asked whether MI5 had ever used women to get close to people they wanted to keep an eye on, it replied: "We would not comment on any operational matters - past or present."