Secret diaries reveal how Home Secretary protected Mitford

Britain's spy chiefs and cabinet ministers were at loggerheads over plans to arrest the society figure Unity Mitford for consorting with Hitler, secret diaries have revealed.

The journals compiled by Guy Liddell, then a high-flying security service director, disclose that MI5 was keen to intern Ms Mitford in 1940 when she returned to Britain after visiting Hitler, whom she idolised.

In disclosures that will reinforce claims that the Mitford family remained influential despite its Fascist links, Liddell said MI5's request to intern her was quashed by the Home Secretary, Sir John Anderson.

Liddell's 12-volume diaries give a detailed account of MI5 activities during the war but will disappoint spy-watchers searching for evidence to support the disputed claim that Liddell, a close friend of Guy Burgess and Kim Philby, was the "fifth man" in the Soviet spy ring inside Whitehall. Liddell discloses only that he had dinner with Philby and makes brief references to meeting Burgess.

In early 1940, Ms Mitford, whose sisters included the novelist Nancy and Diana, the then lover of the Fascist leader Oswald Mosley, shot herself in the head in Berlin in a failed suicide attempt.

Despite political pressure, the Home Office decided that neither Ms Mitford nor her mother, Lady Redesdale, would be stopped when they came back to Britain.

Ms Mitford eventually returned with her mother in April 1940 in a specially commissioned train carriage. She never recovered from her suicide bid and died in May 1948.