Those charged were Harry Houghton, a former naval petty officer, and his girlfriend Ethel Gee, who worked at the Portsmouth dockyard; Gordon Lonsdale, the cover name of the Russian spy Konon Molody; and Peter and Helen Kroger, Americans who had become committed Communists, and who had been involved in the cases of Colonel Abel and Julius and Ethel Rosenberg in America. Those two formed the support cell for the operation run by the Russian intelligence man, Molody.
At their suburban home in Ruislip the Krogers had the high-speed transmitter used to communicate with Moscow, the passport spares and blanks which might be needed to escape, the money and the photographic equipment, while Peter Kroger's role as an anti- quarian bookdealer allowed him constantly to send parcels abroad. Full stops on the pages of many of those books contained microdots giving detail of Britain's underwater defence programme stolen from the Portsmouth dockyard.
As the trial of the five went on, Peter Kroger emerged as a committed Communist who had devoted his life to the cause. Born Morris Cohen in the Bronx in 1911, he became radicalised by the poverty he saw around him, and by international events, soon openly declaring his admiration for the Russian system. He was one of the first to volunteer for the Lincoln Brigade, the American unit which went to fight Fascism in Spain in 1937. He married Helen, who was born Leontina Petkas, in New York in 1941, and though she appeared the dominant partner during their London trial, it was the quiet Peter who converted her, so that she was soon as enthusiastic and as careful an agent as he proved to be.
Kroger was recruited for Soviet clandestine operations while working for AMTORG, the Soviet trading organisation in the United States, in 1941, and was encouraged to join the army when called up the next year. Moscow Centre was preparing him to be an "illegal", an agent in deep cover rather than a national who could rely on diplomatic help.
Reporters covering the 1961 trial found prosecution lawyers immensely helpful in filling in any gaps in the case presented by the Attorney General, and it was thus that Kroger's involvement with Colonel Rudolf Abel emerged - Abel, the head of the Russian apparatus in America, was arrested in 1957. Items found then linked him firmly to the Krogers, and to the Rosenbergs, who had been convicted in 1950. Kroger/Cohen was revealed as a professional agent of long standing on both sides of the Atlantic.
As the case against the five went on, the British public became engrossed by this first picture of the world of professional espionage, with its one-time pads, secret hiding places in tins of talcum powder or lighters, burst transmissions and microdots, and shadowy watchers from MI5. It was the blueprint for dozens of dramas to come. But there was another side too, Peter Kroger the good neighbour, the bookseller who displayed real expertise, the clubbable man who joined in trade cricket matches or suburban dinner parties.
The Krogers served only eight years of their 20-year sentence before being exchanged, and after a spell in Poland, moving to Moscow. Peter kept his faith right up to the end; but, more important, he was a professional. The events of which he was a part informed a generation, and inspired a new form of fiction.
Morris Cohen (Peter Kroger), bookdealer and spy: born New York City 1911; married 1941 Leontina Petkas (died 1992); died Moscow 23 June 1995.