Agent Tricycle's life was a colourful one

One reveals that Stalin may have used the excuse of ill health to "elude dangerous responsibilities" while others outline the underground work of the Communist Party of Great Britain.

Another charts the colourful life of Agent Tricycle - so-called for his love of m�nage a trois relationships.

With his semi-permanent room at the Savoy, string of women and membership of London's most exclusive clubs, the twists and turns of Dusko Popov's life make fascinating reading.

'Lured'

So-called 'Ace of Spies' Sidney Reilly also has a large file which discusses his suitability for intelligence work, carries copies of his marriage certificate to second wife and actress Pepita Bobadilla and deals with his early investigations.

Reilly worked for British Intelligence in Russia after the revolution there but in 1925 he was lured back to the USSR, arrested and executed.

The heroic work of British nurse Edith Cavell is also unveiled for the first time.

During World War I, she was executed by the Germans despite never formally being charged with espionage.

The public opening of the documents is the ninth and largest Security Service (MI5) release.

They are held at the Public Record Office in Kew.