Lawyers for Jeremy Bamber have launched a high court challenge to the Crown Prosecution Service (CPS) in an attempt to force it to disclose evidence they claim could undermine the safety of his conviction for murdering his family.

Bamber is serving a whole life sentence for for killing his adoptive parents, sister and her six-year-old twin boys in 1985.

His lawyers claim the CPS has refused to follow directions made by the court of appeal in 2002 to disclose the material that could challenge his conviction.

It also accuses the CPS of rejecting a report by an eminent ballistics expert appointed by Bamber, without instructing its own expert to challenge the claims.

Nevill and June Bamber were shot and killed inside their Essex farmhouse, along with their adoptive daughter, Sheila Caffell, and Sheila’s six-year-old twin sons, Daniel and Nicholas Caffell.

Bamber, then 24, had phoned the police to say Nevill had phoned him, saying his sister, Sheila, had “gone crazy and has the gun”.

Initially, police believed that Sheila, diagnosed with schizophrenia, had fired the shots then turned the gun on herself.

However, the discovery in a cupboard in the farmhouse of a silencer said to contain the blood of Sheila cast doubt on his claims because it would have made the gun too long for her to kill herself.