The World War II spy who fooled British Nazis into believing he was a Gestapo agent and persuaded them to work for him has been named as a London bank clerk who barely spoke German.

Files released in February by the Security Service, known as MI5, disclosed that the agency used an agent codenamed Jack King to infiltrate groups sympathetic to the enemy. He intercepted top secret information that these “fifth columnists” had hoped to pass to Germany, including about the development of the jet engine and anti-radar technology.

At the time, MI5 refused to give King's true identity. The Telegraph newspaper named him as John Bingham, the spy-master who was the model for John le Carre's long-running character, George Smiley. In documents declassified at the National Archives in London today, King is revealed as Eric Roberts, who until the summer of 1940 was working at the Euston Road branch of the Westminster Bank.

His employers were baffled when MI5 asked if he could be seconded to them. “What we would like to know here is, what are the particular and especial qualification of Mr. Roberts -- which we have not be able to perceive -- for some particular work of national importance?” wrote R.W. Jones, the bank’s assistant controller, in a letter to a man he knew as Lt. Col. Allan Harker. No reply is on the file. MI5 knew things about the 32-year-old Roberts that his employer didn’t.

'Highest Opinion'

“Roberts is thoroughly familiar with everything connected with the various pro-Nazi organisations in this country and Maxwell Knight has the highest opinion of his character and abilities,” an internal memo read.

Knight was an MI5 officer with his own link to fiction: he was one of the inspirations for James Bond’s boss, M, in Ian Fleming’s novels. While the files don’t make clear how Roberts crossed Knight’s path, Knight had spent more than a decade running agents inside British fascist and communist groups. As well as his name and a photograph that shows a bald, unassuming man, the papers include Roberts’s personnel file. He was married with two young sons and had been working for the Westminster Bank for 15 years. He spoke Spanish, could read French and had “slight Portuguese, Italian and German.”

There is also a fake German travel document in the name of Jack King and a 1943 outline of the case written by Victor Rothschild, who was running it.

'Hush-Hush Devices'

Rothschild, writing to the then director general of MI5, David Petrie, was arguing for the continuation of the operation. One page, stamped “MOST SECRET,” spells out how one fascist sympathiser had brought Roberts details of “one of the most secret and hush-hush devices so far developed in the UK.” Thinking Roberts was a Gestapo agent, he gave him details of the “Window” project, which fooled German radar by dropping aluminum strips, an early version of chaff. “It is obvious that the slightest leakage of it to the Germans would put them in a very strong position,” the note read. There is also a hand-drawn map of military positions in the south coast resort of Brighton, provided by a female Nazi supporter.

When the war ended, MI5 decided against prosecuting any of its network of fascists, partly to avoid Roberts having to give evidence. Instead, it allowed them to go to their graves believing they had spent the war working for Germany.

Black Tom

The files also contain new details of the life of a German World War I spy, Franz von Rintelen, who is thought to have set up the group that blew up a munitions depot on Black Tom Island in New York Harbor in 1916 -- the largest explosion in the mainland US until the Sept. 11 attacks. Rintelen had been sent to New York in 1915 to run sabotage operations against shipments of supplies to Europe and Russia. By his own account, he recruited dock workers to plant incendiaries on ships and even set up a union to disrupt the work of the dockyards. He was arrested in England that year, after receiving a message summoning him back to Berlin. In his memoirs, he claimed the message had in fact been sent by the British. In 1917, after the US entered the war, he was sent back to America to stand trial, and sentenced to three years hard labor. The files show him initially congratulated by a former comrade, Admiral Behnke, who wrote that he hoped Rintelen would "always reflect with satisfaction on your activities." He said that while he was, "for official reasons," unable to thank him formally, "I will not refrain from recognising your activities."

No Risk

Having fallen on hard times, Rintelen tried to sue the German government for money that was confiscated from him on his arrest. When this failed, he moved to England. A 1925 MI5 assessment of whether he was a risk concluded that "it seems hardly likely that the Germans would use a person so entirely brule" -- French for burned. Rintelen, now giving himself an aristocratic air by styling himself von Rintelen, decided to sell his story, and in 1933 he published his memoirs, titled "The Dark Invader."

In an unlikely twist, the foreword was written by Admiral Reginald Hall, the former British director of naval intelligence who had captured him. Hall and Rintelen had become friends, with the German attending the wedding of Hall’s daughter the following year. The former saboteur had fallen on hard times and tried to reach out to Adolf Hitler’s new government in Berlin. He suspected his former boss in New York, Franz von Papen, of having betrayed him. Von Papen was now vice-chancellor under Hitler.

Messages to Goebbels

The files contain intercepted messages from Rintelen to Josef Goebbels, Hitler's propaganda chief, urging him to assassinate von Papen, and to make Rintelen ambassador to London. Though some prominent Nazis were killed during what became known as the Night of the Long Knives, Von Papen wasn't among them, and he was instead sidelined to diplomatic roles. As World War II approached, Rintelen repeatedly applied to do intelligence work for the British and was repeatedly rejected. His friend Hall, while affirming that Rintelen was no Nazi, offered the view that he couldn't be completely trusted, either. Rintelen was interned from 1940 to 1945, and on his release he worked as a gardener and odd-job man until his death in 1949.

Bloomberg