Mr Tatchell said he was grateful to have been blessed with "a magistrate with a sense of humour". He was given 28 days to pay the fine and the pounds 320 costs of the case.
His protest during the Archbishop of Canterbury's sermon in Canterbury Cathedral last Easter Day was described as "puerile" by Michael Kelly, the Canterbury Stipendiary Magistrate, who concluded that while it was a breach of the Act it did not merit the maximum penalty of two months in jail.
"It is always difficult to balance the right to protest and the right for uninterrupted services," said Mr Kelly. "I'm sure some people will have been disgusted and deeply offended by your conduct. Some, of course, may have applauded. But I expect that the vast majority will have regarded your conduct as an insignificant and transitory incident in the history of a great cathedral."
Mr Tatchell, the founder of gay pressure group OutRage!, took the microphone from Dr George Carey minutes into his sermon and started delivering his own message to the 2,000-strong congregation. Six fellow protesters held up placards behind him, reinforcing the anger expressed by Mr Tatchell about Dr Carey's attitude to lesbians and homosexuals.
The law under which Mr Tatchell was convicted, which has not been used for 30 years, makes it an offence to commit "riotous, violent or indecent behaviour" in any church building or burial ground. It has its origins in the Brawling Act 1551 which, as a first offence, banned any guilty party from church; cut off an ear for a second offence; cut off the other ear for a third and, in the fourth instance, branded his or her face.
The veteran left-winger Tony Benn was called yesterday as a character witness for Mr Tatchell, whom he has known since 1981. He introduced himself as someone confirmed in the Anglican faith, and proceeded to argue against the church's enjoyment of privileged protection against dissent. Mr Benn recalled an occasion when the former Archbishop of Canterbury, Lord Runcie, attended a meeting in a parish church in his constituency of Chesterfield to answer questions from the congregation about church law. "It is difficult to distinguish between his [an Archbishop of Canterbury's] role as a cleric and his role as a lawmaker - because he is both," he said.
The Labour MP added that sometimes it is necessary to break the law to get it changed, as indeed he had done on two occasions. "The evolution of the law has been much shaped by acts that have been illegal," he said. "Conscience stands above the law because conscience is God-made and law is man-made."
Mr Tatchell said later it had been difficult to challenge the "sweeping and draconian" law. "It seems from his summing up that the magistrate felt obliged to convict me on the basis of case law," he said.
"I have been found guilty in a court of law, but I do not regard myself as morally guilty of any crime."
The Secular Society called for the Act under which he was prosecuted to be abolished. Supporters include the actress Vanessa Redgrave, the author Ludovic Kennedy and the pop star Jimmy Somerville.
The Conservative MP Sir Patrick Cormack said: "It is a derisory fine but his behaviour was thoroughly outrageous and at least it has been recognised that that was the case."
In July, the 10-yearly meeting of Anglican bishops from around the world voted to continue the ban on the ordination of gay clergy.
Tony Benn, Podium,
Brave or Foolish?
Ivan Massow, of Massow Financial Services, which provides advice for gays and lesbians: "He is one of the best crusaders for gay rights. He is hated by straights and almost as much by gays. We need people like Peter Tatchell to push these issues forward."
Matthew Parris, journalist: "Brave but misguided. I admire him. Every movement needs all types. Some of the women who threw themselves under carriages probably went about it the wrong way. I don't agree with his methods but it takes all types."
Paul Burston, gay editor of Time Out and author of Queen's Country: "I don't always hold with everything Peter does, but I think that the way this case has evolved is absurd - that the propriety of a church service is more important than the civil liberties of a group of people."
Simon Fanshawe, writer and broadcaster: "It puts me in a difficult position. I admire someone who gets off their tush and does something but I often think the things he does are so misguided, totally. Peter thinks to draw attention is enough, but it isn't."
Michael Cashman, actor and gay rights campaigner: "Peter is a heroic campaigner. No one can doubt his courage or conviction. I have reservations about the law under which he has been charged as it could ... prevent free speech and expression."
Angela Mason, executive director of Stonewall: "Peter has been campaigning for many years and he is very good at it. He also has great personal integrity, intellect and honesty. We don't always see eye to eye - but no one can doubt his ability as a campaigner."Reuse content