The prime suspect in the case of murdered estate agent Suzy Lamplugh was today due to receive a High Court judge's ruling on whether he has been denied ''free and unimpeded'' access to legal advice.

John Cannan, 48, already serving a life sentence for another murder, has asked the judge to declare unlawful a prison policy governing the exchange of legal documents during visits from his solicitors.

His lawyers complained to Mr Justice Hooper, sitting in London yesterday, that the policy at Full Sutton top security prison, near York, was hampering the meetings.

Cannan, who was given life in 1989 for the rape and murder of Bristol newlywed Shirley Banks, has also been questioned in the case of Miss Lamplugh.

Although the Crown Prosecution Service announced last autumn there was insufficient evidence to charge him, Cannan's lawyers say the police are still following up new leads in the wake of television documentaries about the case screened last November.

Cannan, from Sutton Coldfield in the West Midlands, was also one of a number of suspects questioned in a police re-investigation into the murder of 27-year-old insurance clerk Sandra Court.

Her body was found in a water-filled ditch on the Avon Causeway, near Throop in May 1986 - just eight weeks before Miss Lamplugh's disappearance.

Cannan's counsel Flo Krause told the judge that his client had been subjected to ''regular and intensive'' questioning by the police, making necessary a considerable amount of legal research.

His complaint now was that his access to free and unimpeded legal advice was restricted by the current system of having to make applications the day before a legal visit if he wanted to hand on documents.

Steven Kovats, appearing for the Prison Service, said the Full Sutton policy was necessary for security reasons to prevent the smuggling of unauthorised articles.