Double agents, Communist witch hunts and Nazi plots to flood Britain with false bank notes - all are revealed in the latest batch of secret files released by the National Archive.

This cache of files - the 28th such release by the Security Service - include a total of 86 separate documents.

Among the tales revealed by the release, include the first time that wartime MI6 was infiltrated by a spy working for Germany.

Folkert Arie Van Koutrik was a Dutch man employed in 1940 by MI6, known as the Secret Intelligence Service (SIS), and was sent to work in 1942 at a refugee reception centre in the UK, the files show.

But the files also uncover how in 1946 it was discovered from the interrogation of German prisoners that Van Koutrik had been turned by the Germans in 1938 - and was in fact a double agent.

The information Van Koutrik (known in Germany under the pseudonym 'Walbach') passed to the Nazis led to the capture of British officers Richard Stevens and Sigismund Best by the Gestapo at Venlo in 1939.

The post-war inquiry reported that the double-agent had 'blood on his hands'.

Another file contains allegations that Herman Goering might have attempted to pass war materials to the British for money.

Via a supposed relationship with a British lawyer and a "somewhat shady" Latvian banker, the file says that Goering was "essentially corrupt" and might be turned to "lend himself to a conspiracy with the enemy".

In another it is revealed how MI5 was baffled to discover there were no records of Charlie Chaplin's birth when it investigated his alleged communist sympathies.

British intelligence officers could find no documents confirming the silent film star was born in London in April 1889, and they dismissed claims that he was in fact originally from France.

The mystery of Chaplin's birth emerged when the US authorities asked MI5 to look into the comic actor's background after he left America in 1952 under a cloud of suspicion over his communist links.

A plot by the Nazis to ruin the British currency and aid a possible invasion are also revealed in the cache of files.

Nazi forgers succeeded in flooding Europe with fake British bank notes, "destroying" confidence in the UK currency, the files show.

By the end of the Second World War the forgeries were so rife, British bank notes would not be accepted on the Continent.

"At present no one will accept a Bank of England note in any neutral country of Europe except at a very large discount’," the files say.

The Germans first began forging the notes in 1940 in preparation for Hitler's planned invasion of Britain, according to a report drawn up in 1945 by Sir Edward Reid of MI5's section B1B.

According to a captured German agent, the plan was to scatter the notes over the country from the air "in order to create loss of confidence and general confusion".

Although Hitler was forced to abandon his invasion plan after the failure of the Luftwaffe to gain aerial supremacy in the Battle of Britain, the German forgers carried on perfecting their techniques to devastating effect.

Yet another file reveals the tale of the 'Gestapo Lawrence' Franz Wimmer-Lamquet, who gathered a "desert army of 3,000 Arabs against the Allies" and had them drive around in Jeeps dressed as American GIs to attack Arab chiefs, leaving a "trail of hatred" for the 'American' attackers.

Japanese espionage in Malaya and investigations into the Communist backgrounds of prominent scientists are also discussed.

The documents will be available to download free of charge from the National Archive for one month.