Was it appropriate to make this woman talk?

"Appropriate adult" is an odd title for an odd job. Janet Leach, Fred West's "appropriate adult", was a charity worker in her late thirties who volunteered to sit in on police interviews with West, but probably had no idea what it would turn into.

It is a role created and named, but not adequately defined, in the 1984 Police and Criminal Evidence Act, which set the rules for the preparation of prosecutions. The idea was that children, or adults with mental difficulties, should not be left at the mercy of the police, who might lead them to incriminate themselves. The task of the appropriate adult is to advise the accused, ensuring that an interview is conducted properly, and that the suspect can take legal advice if he or she needs it.

Perhaps the most notorious example of a suspect with learning difficulties left unprotected was Stefan Kiszko, who confessed to raping and killing an 11-year-old girl, although tests proved he could not have secreted the sperm found on the girl's clothes. He was released on appeal after several years in prison.

The police are supposed to call in an appropriate adult whenever they think that someone may be vulnerable, and therefore at risk of being led into an unsound confession by the police. The police don't appoint appropriate adults as often as the mental health charity Mencap believes they should, but the price they can pay is that judges sometimes exclude confessions made in the absence of an appropriate adult, and have dismissed cases on that basis.

It will not normally be the ordeal it turned into for Mrs Leach. She has to sit in on hours of interviews about the inhuman goings-on in Cromwell Street, listening to West talk about sex between combinations of inhabitants, children and adults, about cruelty and killings. Mrs Leach, who has five children of her own, had a stroke in June, and when she had to go to court to give evidence about her experiences she collapsed again.

The appropriate adult will normally be a relative or guardian of the suspect. Failing that, where else do the police find a likely candidate? According to Penny Letts, secretary to the Law Society's mental handicap and disability committee, it is not always easy. The job is voluntary and unpaid, with no qualifications specified by law, and different police forces have different policies. Often, duty social workers are called in, but in a long process such as the West trial, a social services department will often say it cannot spare a social worker full-time for weeks. Other forces have lists of suitable volunteers.

The role of the appropriate adult is different from the solicitor's. Their protection is of a different, strictly legal kind. A solicitor has no choice but to take the advice of the client: some clients may choose to dismiss their solicitors and confess to a friendly policeman.

As the case of Mrs Leach and Fred West shows, there is a potential conflict of interests which the 1984 Act does nothing to prevent. The suitable adult must not be a police officer, it says, so the intention is clearly that the adult should be on the suspect's side. Nor should he or she be a solicitor. But while the solicitor is protected by law from having to disclose anything a client says, the appropriate adult is not.

It must look different to the suspect in the police cell, who will probably think he can have conversations with the adult in confidence. As the court in Winchester heard, Fred West allegedly confided a great deal. Mrs Leach was present during scores of interviews with the police, and developed a rapport with West. Then the police called her to tell the court about her conversations. She said he told her that he had agreed to "take the blame for everything" to protect his wife, who would say nothing.

Under the law she had no option but to testify. A working party of lawyers, police and mental health experts this year recommended that an appropriate adult should be given the same confidentiality as a solicitor. The Home Office is considering the suggestions, and may change the law. Until then, an appropriate adult is probably not an appropriate person to confide in.