Five German spies who were captured in the Second World War and persuaded to become double agents, working for the British, have been identified from released MI5 files, despite a longstanding taboo on naming agents.

The uncovering of the identities was made by a researcher who studied MI5 files released to the National Archives in Kew and cross-referenced relevant documents to find the names.

David List told the BBC Today programme that it had not been difficult to work out who the secret agents were from cross-checking all the files that related to their capture and interrogation at a special centre run by MI5 during the war. “It was just basic, hard graft (and) due diligence,” he said.

Both MI5 and MI6 hold to the absolute rule that they will never divulge the identity of secret agents - men and women who are recruited by intelligence officers to act as their eyes and ears in gathering secret information.

However, unlike MI6 which has kept all its intelligence files locked up at its headquarters in London, MI5 launched a new policy of openness some years ago and announced that it intended to release files that were at least 50 years old over a phased period. The National Archives has received more than 3,500 MI5 files since the late 1990s.

MI5 recognised that there was always a risk that some astute historian or researcher might be able to work out the possible names of agents by cross-checking files. However, as a security source said yesterday: “We’re still never going to confirm or deny the identity of a past agent, so even if a researcher claims to have uncovered a name, MI5 will never comment.”

Mr List’s endeavours focused on MI5 files that detailed prisoners who were taken to the famous wartime interrogation centre, Camp 020, based at Ham in Surrey. One document revealed all the arrivals and departures of captured spies at Camp 020, including their real names.

The forbidding Camp 020 buildings at Latchmere House in Ham were used to interrogate enemy spies captured in Britain. It was commanded by Lieutenant-Colonel Robin “Tin Eye” Stephens, so named because he wore a thick monocle.

Camp 020 played a crucial part in MI5’s legendary Double Cross system under which German spies sent to Britain to gather intelligence on the war effort, were turned by interrogators and persuaded to betray their country and serve as double agents. For the Double Cross programme, MI5 worked closely with Section V, the counter-espionage branch of MI6.

Over the years names of some of the double agents have emerged, although never from MI5. Some of the wartime spies have written books of their exploits. The most famous double cross agent was Jean Pujol, a Spaniard codenamed Garbo, who played a vital role in deceiving the Germans into believing that the Allies planned to launch their main invasion of France in the Pas-de-Calais, and that the Normandy landings were a diversionary tactic.

Stephen Dorril, an author of intelligence books, told Today: “It’s really surprising that here is a file that can be used to identify agents.”

However, the security sources said that every effort was made to redact the names of agents in files handed over to the National Archives. “We’re incredibly cautious about releasing documents but we can’t stop people trying to cross-reference files to see if they can identify agents,” one source said.

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