It seems things were patched up briefly between the British party and my father in mid-1941 when Germany invaded Russia and Stalin became good old Uncle Joe. The file was officially closed on February 28, 1945. Yet, to my surprise the National Archives assert that it was not until "the late Fifties that he appears to have become disillusioned with Communism".

How do they know, unless informed by MI5? In fact, as the Cold War hotted up, father joined the Labour Party and was firmly opposed to Russia. In 1948, so father told me, he contacted Pollitt and said that if Czech comrades, then being purged as Zionists or Titoists were harmed, he would break his silence, hand over documents and tell all to the Security Service. Pollitt warned him off: "Never forget, Johnny, we run British Intelligence." An ill-judged threat, for father turned instead to the fledgling CIA. That may explain why he was given exemption from regulations banning Communists and ex-Communists from the US.

One further twist. I recall father's contempt for those British Communists who finally left the party after the Hungarian Revolution in 1956. They had, he said, been too cowardly or too morally blind to have recognised the horrors of Stalinism by 1939. Yet I also remember his friendship with Boris Averyanov, a regular visitor to our home in the Fifties. He was Soviet labour attaché in London, in reality the KGB resident, orchestrating the activities of Communist union bosses, several of whom were also our family friends. And then there were visits from Anna, the charming sister of the nuclear spy Bruno Pontecorvo.

Was father keeping an eye on this motley crew for the CIA? Could he have been a British double agent? His file is labelled Vol 1. Is there a Vol 2 locked away in MI5's vaults? I doubt I will ever know. Obviously there are questions still unanswered. But he was not - as far as I can tell - called upon to commit acts of treason or moral turpitude. He was not murdered, as some defecting agents were. He was a brave and honourable - if occasionally misguided - foot soldier in the fight against National Socialism and, later, against Soviet imperialism. I can live very happily with that. I hope my family can.