WWII spy sea capture planned

German double agent Alexander used a number of aliases

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British security services planned an "exceptional" sea capture during World War II of arguably Germany's most successful double agent, MI5 files reveal.

The Austrian, referred to by his alias Jean Alexander, supplied information to Germany while working for Czech intelligence in Portugal.

British security service suspicions were first aroused in 1942 when Alexander was believed to have handed over to the Germans a wireless transmitter intended for Allies in Paris, the files released to the National Archives suggest.

The service was concerned his "continued presence in Lisbon constitutes the gravest menace to British interests" and that he should be "lured to this country for interrogation".

'Cry wolf'

However rivalry between the British and Czech intelligence services appears to have hindered this.

A document states: "The Czechs had not been easily persuaded that the case against Alexander was conclusive.

The capture...would be of such high importance as to justify exceptional measures

"They had had bad experiences in the past in connection with agents who had been reported to them as bad and had subsequently been taken on by SIS (the Secret Intelligence Service - MI6) themselves.

"In these circumstances they had looked upon the warning against Alexander as 'cry wolf'."

Subsequent investigations found Alexander had betrayed to Germany several Allied networks in occupied Europe, including in Paris and Marseille in 1941, causing the "death of many members of the French underground".

High seas interception

The double agent had "pulled off the unusual achievement of handing over to the enemy an Allied intelligence service complete with agents, couriers, ciphers and wireless equipment. He is, in fact, an enemy agent of the highest calibre".

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This discovery led to Alexander's expulsion from Czech intelligence, but he then "managed to gain the confidence of the Americans who employed him for some time".

Around 1943, America agreed to "make an attempt to induce Alexander to travel to the US on condition that we remove him en route".

A letter, presumably to naval commanders, says: "I know that in normal circumstances you are strongly opposed to the interception of neutral vessels on the high seas. But I would urge you to consider this as an altogether exceptional case.

"The capture of Alexander would be of such high importance as to justify exceptional measures."

Alexander's file contains a reply agreeing to the plan, but for reasons not recorded it never went ahead.

Lisbon arrest

Alexander continued to serve Germany, from various countries and using various aliases, for the rest of the war. He was captured in Lisbon by Interpol in 1946.

Alexander was an 'extremely plausible' double agent

In a 34-page statement from Alexander's initial interrogation by the US in Stuttgart, he insists he had been working as a double agent for the Allies.

"He is so extremely plausible," a subsequent document says.

Referring to Alexander and a second prisoner, it suggests that "unless they are dealt with by really competent and well-briefed British interrogators there is a distinct danger of them becoming an active intelligence menace once again".

Subsequent documents show Alexander eventually admitted most of the activities he was accused of, and was freed in 1947.

Members of the public can view the 280 newly-released files at the National Archives, Kew, west London.