A former church warden serving a life sentence for killing a university lecturer following a campaign of physical and mental torture should have his murder conviction overturned, senior judges have been told.

Benjamin Field, 30, was found guilty of killing Peter Farquhar, 69, in order to inherit his house and money after driving him to think he was losing his mind following a period of gaslighting.

Field, of Wellingborough Road, Olney, Buckinghamshire, was ordered to serve at least 36 years behind bars in October 2019 after being convicted of Mr Farquhar’s murder following a trial at Oxford Crown Court.

At a Court of Appeal hearing in London on Thursday, Field’s barrister David Jeremy QC argued that the trial judge, Mr Justice Sweeney, misdirected the jury and the murder conviction is “unsafe” as a result.

Mr Jeremy told the court the directions given to the jury before it started its deliberations left the defence with “nothing to say” when in fact there was “much that could be said on Field’s behalf on the issue of causation”.

He said full directions would have explained to jurors the fact that the prosecution “could not prove causation” because there was “no evidence that Mr Farquhar had been forced or tricked” into consuming alcohol and a tranquiliser drug.

Oliver Saxby QC, who represented the Crown Prosecution Service, contended that the jury’s verdict on the count of murder is safe.

He said that the drugs, alcohol and “smothering” were all part of a plan concocted by Field.

The prosecution case at trial was that Field secretly gave Mr Farquhar drugs and spiked his whisky, hoping that his eventual death at his hands would look like suicide or an accident.

It was only when the Baptist minister’s son began targeting Mr Farquhar’s neighbour, Ann Moore-Martin, in the village of Maids Moreton, Buckinghamshire, that his wicked scheme began to unravel.

The sexually promiscuous Field also manipulated Miss Moore-Martin, a deeply religious retired head teacher, by writing messages on her mirrors purporting to be from God.

He admitted fraudulently being in relationships with the pensioners as part of his plan to get them to change their wills.

Mr Farquhar, who was torn about his sexuality because of his religion, died in October 2015 while Miss Moore-Martin died in May 2017 from natural causes.

Field underwent a “betrothal” ceremony with gay Mr Farquhar while also having a string of girlfriends and was in a sexual relationship with Miss Moore-Martin, who was 57 years his senior.

Miss Moore-Martin gave him £4,000 to buy a car and £27,000 for a dialysis machine.

Field admitted two counts of burglary and three of fraud before his trial for murder.

He was found not guilty of conspiracy to murder Miss Moore-Martin and an alternative charge of attempted murder. He was also found not guilty of possession of an article for use in fraud.

Two psychiatrists said Field was either suffering from a narcissistic personality disorder or a psychopathic personality disorder.

Sentencing Field, Mr Justice Sweeney said he “lived by deception and deceit and had been a well-practised and able liar”.

“You further admitted how you could manipulate and manoeuvre people, however sceptical they may have been, to achieve your ends without ever asking them to do so directly,” he said.

“You were, you accepted, a snake talker, as you were able to build pressure on your victims to believe what you needed them to believe and then to do whatever you needed them to do.

“The evidence at trial clearly demonstrated grandiosity, a sense of superiority towards others, the exploitation of others to achieve personal gain, the need to belittle and humiliate others, fixation on fantasies of power and success, intelligence, a need for admiration from others, and a sense of entitlement together with an unwillingness to empathise with the feelings, needs and wishes of others.”

The judge said that Field murdered Mr Farquhar by covertly giving him drugs and getting him to drink strong whisky and then, “if it was necessary, finished him off by suffocating him in a way that left no trace”.

Lord Justice Fulford, who heard the appeal with two other judges, said they will give their ruling at a later date.