Moors murderer Myra Hindley formally petitioned the Government from her Rochester prison cell to allow her to be hypnotised - in the hope it would help locate the body of victim Keith Bennett.

The letters from Hindley to the then Home Secretary Douglas Hurd were among thousands of documents in 600 files on Hindley made public on Wednesday at the National Archives.

In one letter dated December 11, 1987, Hindley wrote from her cell at Cookham Wood Prison : “I now wish to urge you to reach a positive decision [on hypnosis] and grant the request.

“If the proposed hypnosis is unsuccessful, at least it can be said that everything humanly possible has been done.

“If it is successful the immeasurable relief it will bring to Mrs Johnson [Keith’s mother], the fact that the police can finally close the file on the whole case, and the benefit to society knowing at last that the Moors case, which has haunted the psyche of the nation, is finally resolved and exorcised, will be no small matter.”

Hindley offered to pay for the hypnosis herself, but Douglas Hurd refused.

Keith Bennett was just 12 when he became the third victim of Hindley and Ian Brady in 1964.

His body was buried on Saddleworth Moor outside Manchester and is the only body never recovered.

Among other information that emerges from the files are details about Hindley’s struggles with fellow inmates-turned-informers who sold her out to the press, her declining health and her complicated relationship with Brady.

Hindley died in 2002 of a chest infection following a heart attack.