Man with a double life: Alfred Charles "Johnny" Torode with his son John, the author of this article, outside their Ilford home in 1958

It's official. My father was a Soviet agent. MI5 says so. Decades after his death, the spooks have finally released his security file to the National Archives. It contains a damning judgment: "There is not the slightest doubt that he is one of a very small group of senior and trusted couriers" working for the Comintern - the murderous agency which Stalin used to control world Communism. I had long since guessed as much. But my suspicions disturbed my family. That hurt because I remember father as a responsible, well-regarded union leader, and a loving, deeply moral, family man. The last thing I wanted was to trash his reputation.

I learned that the file had been released because the National Archives placed a curious one-paragraph "description" of it on their website. The file on Alfred Charles "Johnny" Torode was opened on September 19, 1932, supposedly because he had "come into contact with known Communists" a year earlier. Yet "coming into contact" with Communists was surely not reason enough to open a file on an obscure 24-year-old East End signwriter? And he was accused of using a string of deeply unconvincing aliases - Trode, Terrode and, bizarely, Love. My mother, née Schreiber, was said, equally farcically, to have passed herself off as Schneider. The only specific charge against my father in the brief description was that by 1935 he was "carrying money between the UK and Scandinavia". Of course Moscow gold was flowing between the USSR, via Scandinavia, to Western Europe by courier - but mainly into Nazi Germany. Of course money came to (not from) the UK - but seldom manually. Soviet subsidies to the Communist Party of Great Britain (CPGB) came mainly via banks and "front" companies in London. Had MI5 lost the plot or were researchers being misled?

At least I was now sure that father had been leading a double life. But the description was nonsense. I had to visit the National Archives and read his file.

What did I already know? Well, father was to become general secretary of his small but powerful trade union, the Sign and Display Union, in 1938, and remained there until he retired. But in the early Thirties, he was a young man from a family of bricklayers and house painters. Some 30 years ago I inherited his first passport, issued in 1928. Over the next five years he made an astonishing eight trips to France. Holidays perhaps? But it seems unlikely. Was something more sinister already afoot? In 1933, Hitler came to power, and father joined the British Communist Party. By that summer, German comrades were in Dachau, Moscow or deep underground. And that was when father's double life really began.