Convicted murderer Jeremy Bamber has launched legal action over a refusal by the prison service to downgrade him from maximum security.

The 59-year-old is serving life after being found guilty of murdering his adoptive parents Nevill and June, both 61, his sister Sheila Caffell, 26, and her six-year-old twins Daniel and Nicholas at White House Farm, Essex, in August 1985.

He has always protested his innocence and claims Ms Caffell, who suffered from schizophrenia, shot her family before turning the gun on herself.

Bamber is seeking a legal challenge at the High Court over a decision taken in March by the director of the long-term and high security estate – part of the prisons and probation service – not to downgrade him from a Category A prisoner, or to direct that an oral hearing on the issue take place.

Category A prisoners are considered the most dangerous to the public and held in maximum security conditions.

At a remote hearing on Monday, lawyers for Bamber asked Mr Justice Julian Knowles to grant permission for a full hearing of Bamber’s challenge, arguing that the decision was “unreasonable”.

In written documents before the court, Bamber’s barrister Matthew Stanbury said his client, who is being held at HMP Wakefield, “is a model prisoner”.

“He acts as a peer mentor teaching other prisoners to read and write,” Mr Stanbury said.

“He has a partner and support network within the community.”

Mr Stanbury said an independent psychologist’s report, commissioned by Bamber’s solicitors, concluded he had met the test for downgrading a Category A prisoner and that these conditions were “no longer necessary” for managing him.

He argued that the decision not to downgrade Bamber from Category A was “unreasonable” as it “substantially misrepresented” the opinion given by the independent psychologist.

He also said that “fairness required an oral hearing” over whether Bamber should be downgraded, for reasons including the fact that he “has served 35 years without ever having an oral hearing, and the passage of time means that a risk assessment is more difficult without a face-to-face assessment”.

The Ministry of Justice is opposing Bamber’s action.

The challenge is the latest action in his long-running battle to clear his name.

He had an appeal against his convictions dismissed by the Court of Appeal in 2002, and also had a High Court challenge to the Criminal Cases Review Commission’s (CCRC) refusal to refer his case for another appeal rejected in 2012.

Bamber is in the process of pursuing a fresh application to the CCRC.

Mr Justice Julian Knowles reserved his ruling to a later date.