Nicholas Brock, 57, a far-right sympathiser from Maidenhead, Berkshire, is currently serving a sentence for possessing terrorist materials. He is alleged to have threatened to kill a prison officer at HMP Bullingdon after his complaint about food was not heard. He also denies making threats against a probation officer.

Oxford Crown Court heard that Brock had a “very strong issue with jacket potatoes”. Prison officer Oliver Kelly told jurors: “Mr Brock would get quite angry if there was something wrong with his food. He has dietary requirements and sometimes the kitchen makes mistakes. He would complain about this to the senior prison officer, Mr Christopher English. But at the time, as we are trying to control 180 prisoners to get their lunch, Mr English didn’t have time to speak to Mr Brock and that made Mr Brock angry.”

The defendant is alleged to have said: “I will put a 9mm to the back of his head. Don’t think I won’t do it.”

Prosecutor Emma Gargitter said Brock had claimed he owned deactivated firearms and “knew people who could reactivate them”. She added that he was hostile to his probation officer, Saiqa Yasmin, “in part because of her race”, and that he had complained she was preventing him from doing anything on release.

When another probation officer told him they would look into his concerns, he allegedly asked: “Are you going to shoot her?”

Before adjourning, Judge Nigel Daly remarked: “I’m really curious to know what was wrong about the jacket potato.”