Police have arrested the mental health advocate of Moors murderer Ian Brady following her disclosure that he gave her a letter that may reveal the whereabouts of a child’s body missing since 1964.

Jackie Powell, 49, was arrested this morning on suspicion of preventing the burial of a body, but has now been bailed pending further enquiries.

Police seized papers from Powell’s South Wales home after she told the makers of a TV documentary that Brady had given her letters to be opened after his death. One of these letters is addressed to Winnie Johnson, mother of Keith Bennett. The child was 12 years old when abducted on 16 June 1964; his body, alone among the five victims of the Moors murderers, has never been found.

Powell told the documentary makers that the letter could contain ‘the means to her [Bennett’s mother] possibly being able to rest’. Greater Manchester Police said that they do not have any new information about the location of Bennett’s body.

Ian Brady and his accomplice Myra Hindley abducted and murdered five children between 1963 and 1965, burying their bodies on Saddleworth Moor near Manchester. Four of the bodies have been recovered, but Brady has consistently refused to reveal where Bennett was buried.

Since April 2009, statutory access to independent mental health advocates has been available to patients, such as Brady, detained under the Mental Health Act 2007. Their role is to help patients understand and exercise their legal rights, express their thoughts and to support them at interviews.

They are not lawyers, despite the word ‘advocate’ in their job title, and so are not subject to legal privilege. Even if they were lawyers, in a case as serious as this, privilege would have been waived and they should have told police about Brady’s letter.

Speaking to the Radio Four Today programme this morning, Law Society President Lucy Scott-Moncrieff said that mental health advocates ‘are not lawyers and privilege does not apply here’.