Oxfordshire heiress Diana Mitford, the wife of British fascist leader Sir Oswald Mosley, was deemed more dangerous than her husband, according to formerly secret documents just released.

Sir Oswald was the leading figure in the British Union of Fascists and was interned, along with Lady Diana, between 1940 and 1943.

But an anonymous source quoted in another CID document claimed: "Lady Mosley is said to be far cleverer and more dangerous than her husband and will stick at nothing to achieve her ambitions -- she is wildly ambitious."

Further documents revealed the contents of a conversation between CID officers and Sir Oswald during inquiries about his party's finances.

The papers show Sir Oswald believed he would be assassinated when the threat of war became imminent.

Sir Oswald told the officers that he had met Adolf Hitler twice and did not think the German Nazi leader wanted to harm England in any way.

One officer described Sir Oswald as "immensely vain, a bad judge of men, extremely urbane and cunning".

Lady Diana, who grew up with her sisters at Swinbrook, near Burford, acted as a go-between for Sir Oswald and Hitler and was herself interned a fortnight after her husband.

The documents were published on November 28 by the Public Records Office in Kew, west London. On his arrest, Special Branch officers found three handguns, two rifles, two shotguns, two duelling pistols, a sword and a truncheon.

The documents stated: "He did not think that Hitler wanted to smash the British Empire."