A body modification artist who called himself Dr Evil has admitted inflicting grievous bodily harm on three customers by carrying out a tongue-splitting procedure and removing an ear and a nipple.

Brendan McCarthy, 50, changed his pleas to guilty at Wolverhampton crown court on Tuesday after a two-year legal fight in which he unsuccessfully claimed that the consent of his customers provided him with a lawful defence.

McCarthy, from Bushbury in Wolverhampton, carried out the ear removal at his studio in 2015 without using anaesthetic, three years after he split a woman’s tongue with a scalpel and removed another customer’s nipple.

When he first appeared in court in 2017, he denied six counts relating to the three procedures on the basis that the procedures were consensual.

But the judge, Amjad Nawaz, ruled that the registered tattooist could not use his clients’ written permission as a defence. Nawaz based his decision on precedent set by previous prosecutions, including one in which a husband branded his wife’s buttocks with a hot knife.

McCarthy took his case to the court of appeal but it was rejected. In their 12-page ruling, the three appeal court judges, including the lord chief justice of England and Wales, accepted that the ear removal had been done quite well but said it was not in the public interest that a person could wound another for no good reason.

Their judgment read: “There is, to our minds, no proper analogy between body modification, which involves the removal of parts of the body or mutilation as seen in tongue-splitting, and tattooing, piercing or other body adornment. What the defendant undertook for reward in this case was a series of medical procedures for no medical reason … The personal autonomy of his customers does not provide the appellant with a justification for removing body modification from the ambit of the law of assault.”

McCarthy was refused permission to appeal to the supreme court.

An online petition set up to support the “knowledgable, skilful and hygienic” body modification artist claimed the case was a threat to “the right to express ourselves in whatever modified manner we wish in a safe environment” It was signed by more than 13,000 people.

Adjourning the case for the preparation of a pre-sentence report, Nawaz told McCarthy: “These are serious matters. Ordinarily a sentence of custody would be inevitable but there are differences in this case.”

McCarthy was bailed with a condition that he does not undertake surgical procedures. He will be sentenced on 21 March.

Tattoo artists and piercers have to be licensed by local authorities but there are no formal qualifications. Some have called for body modification procedures to be regulated amid concerns they are becoming more extreme.