A SPY who betrayed the secret of the atom bomb to the Russians used parts of Kew to leave secret messages, new files released by the National Archive reveal this week.

The files tell the story of Klaus Fuchs, one of the most significant communist spies of the Cold War, who worked on the development of the atom bomb in America and passed on its secrets.

Among the files, which detail how he was investigated by the British Security Service are some that outline how Fuchs used a number of locations in Kew to communicate with his contact using chalk marks and a copy of Men Only' magazine.

Fuchs was born in Germany and was a member of the Communist Party who fled to Britain in 1933 following the rise of the Nazi Party. In 1943 he went to the United States to work on the development of the atom bomb at Los Alamos, after the war returning to Britain where he worked at the Atomic Energy Research Establishment in Harwell.

However, between 1942 and 1949 he had worked for Russian intelligence, passing on information about the atom bomb to a number of KGB and GRU case officers. The atom bomb which the Russians announced to the world after Fuch's trial was a virtual facsimile of the Anglo-American bomb and had been built using information supplied by him.

Fuchs was arrested in 1950 following information gleaned about an agent matching his details. He confessed on January 23rd, although no actual evidence of his espionage was uncovered by the investigation. He was tried and sentenced to 14 years imprisonment, and died in 1988.

Revealed in the National Archive's files (formerly the Public Record Office) is the recommendation by Special Branch that every foreign national living in the Richmond area should be investigated after his arrest. The report contains details of eight people who were investigated in an attempt to discover who his contact was, including a doctor, a socialist engraver from Germany, a businessman and a botanist at the Royal Botanical Gardens. Yet no-one was ever caught.

Investigating officer WJ Skardon explains the Kew communication arrangements in a report which states: "I am now clearer on vexed question of chalk marks. In the event of any rendezvous falling through Fuchs would make a fresh arrangement by dropping a copy of Men Only' magazine into the garden of 166 Kew Road.

"Before he did this it would be his duty to report to the entry near Kew Gardens Station (Station Approach) and if he found there was a cross in chalk on the wall this would indicate that it was dangerous to throw the book into the garden. When he had thrown the book into the garden he would put a chalk mark on the fence in Ennerdale Road to indicate that he had done so.

"In fact this arrangement was only tried out on one occasion and was never used in practice but Fuchs understood that if the chalk mark appeared in the said entry that he would delay action until it was no longer there."

The officer believed that when this system was first established it was designed as a means to pass on information but eventually existed simply to provide an alternative or emergency means for Fuchs to make contact with his spymaster.

Fuchs said he did not know who lived at 166 Kew Road and although it was believed they were involved, they were never caught.

There are also details of a detour to Kew which took place on June 27th 1950 during his transfer between Wormwood Scrubs to Stafford Prison. Officer WJ Skardon reported: "On arrival in Kew and in accordance with my instructions he took over the task of directing the driver and indicated unerringly that the three places were as we had understood them to be. At the side of a shop in Station Approach (the place for a chalk mark to cancel a meeting), in Ennerdale Road (for the chalk mark to indicate that the magazine had been planted) and at 166 Kew Road, pointing out the garden there as previously described.

"He carried out this identification without hesitation and the whole operation from the time of arrival at Kew Gardens was three minutes."

Surveillance reports on Fuchs also reveal that he had spent a night with his suspected lover, Erna Skinner at the Palm Court Hotel in Richmond, which was demolished over 25 years ago.

Howard Davies, of the National Archive, who is responsible for selecting the records, explained why he believed Kew was chosen. He said: "It was convenient, it must have been somewhere both he and his contact were frequently passing for it to work, for it only works if someone is passing every day.

"They never caught the contact. They caught the people in Russia who received the information, but never the intermediary."

Members of the public can view these and other documents at the National Archive.