The history teacher said he was on his way home from worshipping at New Road Baptist Church, and had not planned to attend the event.
Mr Hill, who is also the campaigns manager at the Peace Pledge Union, said he reacted after the High Sheriff made the order, and that several members of the public told him to “shut up”. He also claimed that he had stayed silent during a speech, which mourned the loss of Queen Elizabeth II.
Speaking to NationalWorld, he said: “I found [the proclamation] was something that I couldn’t just say nothing about. So when they read it out, I called out, ‘who elected him?’ And a couple of people chatted, told me to shut up, which I thought was fair enough.
“I responded that I thought a head of state was being imposed on us without our consent”, he said.
Two security guards reportedly then told him to “be quiet” and then allegedly pushed Mr Hill out of the way. He was then ushered away by police officers. Mr Hill said that they supposedly handcuffed him and led him into the back of a police van.
Mr Hill, who is the author of Peace Protesters: A History of Modern-Day War Resistance, asserted that several people attempted to intervene in support of him. He said: “These weren’t anti-monarchists, these weren’t activists. Some of them were people who had come for the proclamation.”
He added: “There were two men who more or less followed the police as they’re arresting me and saying, “Why are you arresting him? I don’t agree with his views, but surely he’s got a right to free speech?””
He said there was then further confusion about the reason for his arrest. Mr Hill reported that police officers initially detained him under the Police, Crime, Sentencing and Courts Act 2022. Thames Valley Police, however, then issued a statement saying Mr Hill was arrested on suspicion of a public order offence, Section 5 Public Order Act.
Mr Hill said he was “gobsmacked” at the arrest, despite having been previously arrested for nonviolent direct action as a former media coordinator for Campaign Against the Arms Trade. He said: “I wasn’t surprised I was arrested then. I was doing direct action. I planned to do something that I knew might have that sort of consequence.
Mr Hill admitted: “This time, I was really gobsmacked. I literally called out one sentence in a public place in what is a fairly liberal city.
“I was really alarmed because somebody, whether or not the police charged me, whether or not they arrest other people, if fear of arrest stops people protesting, then that’s already suppressed democracy”.
A Thames Valley spokesperson said: “A 45-year-old man was arrested in connection with a disturbance that was caused during the county proclamation ceremony of King Charles III in Oxford.
“He has subsequently been de-arrested and is engaging with us voluntarily as we investigate a public order offence.”