There was nowhere quite like the Vox Cafe in Tangier. It resembled a scene from Casablanca.

At the bar, sweaty, white-suited intelligence officials from half a dozen nations drank - and as they did, they spilled both booze and secrets.

The Vox was just the right place to be. With Tangier held by Spain in 1940, and out of the war, it was where British, German and Italian spooks could rub shoulders in an attempt to winkle out each other's war plans.

Intelligence was the currency and the bar's "mine host," the unfortunately named Carl Marx, who had fled from Nazi-controlled Saar in France, made good use of it.

He became an informant for the French, the Italians (until they became part of the Axis) and the British.

But Secret Intelligence Service documents released this week by the National Archives showed that, in the murky world of espionage, Marx - who went on to become the JC's Rhineland correspondent - was accused by MI6 of consorting with the Germans.

In a letter marked "secret", a British agent told his masters that it was "well known that Marx, a Jew and the grandson of the man of the same name who founded the First International and wrote Das Kapital, has been working for the Germans in Tangier." He was, of course, nothing of the sort.

Accusations were nothing new to Marx. When he was living in Rome in 1938, the Italians locked him up for double-crossing them with the French. He was also accused of people-smuggling - helping Jews on the run from the growing threat of Nazism.

But allegations of consorting with the Nazis were of a very different order. When, in 1942, he fled to the UK via Gibraltar, he was interned and later held in Brixton Prison, accused of being a German agent.

Marx wrote a lengthy document accusing British agents of an "extraordinary mistake," and insisting they had been told in advance when he contacted the German consulate in Tangier, and had benefited as a result.

Contacts with the Germans had begun when he received a summons from the German consulate. He protested he was anti-Nazi, but Gestapo agent Max Paul Bartle, was unmoved. Fearing for his safety and that of his friends, Marx continued the contacts he hoped would produce valuable data for British intelligence.

Yet, when he contacted a British agent to arrange escape to the UK, he was told: "Let the Germans send you."

At first M16 officials were not convinced of his loyalty and antisemitism reared its head. In one analysis, he was described as a "small, miserable Jewish type with a typical large Jewish nose."

Another said he was "a completely unscrupulous international crook."

After interrogations, M16 accepted he had contributed to British intelligence. But the praise was grudging.

In a report an agent said: "Because he is of Jewish origin it is not a guarantee of anti-Nazi convictions. We know of other examples of Jews engaged in espionage for the Germans. In fact their Jewish origins afford them excellent cover.

"… I feel that anti-Nazi sentiments would not necessarily prevent him from working for the Germans if temporary profit or personal safety could be derived by doing so."