IT WAS during a rehearsal in the Arc Pentecostal church in Stratford, east London, that Samuel Taveres first noticed one of his choristers was possessed by a demon. Approaching cautiously, the young preacher asked the demon’s name. It had an answer ready, using familiar words from an exorcism scene in the New Testament: “I am legion”. “This meant,” says Mr Tavares, “that a lot of different demons were in there.” The choir spent the rest of the day praying and commanding the spirits to leave the woman, who was also schizophrenic. It was a struggle, says Mr Tavares, “and I’m not sure she is fully delivered even now.”

Such dramas are not unusual in Pentecostal churches: many offer weekly exorcisms. The faith, popular among Britain’s African and Brazilian populations, as well as many white Britons, was the country’s fastest-growing Christian denomination in 2005-15. But a connection to child abuse in some startup African Pentecostal churches is troubling the police. Jean La Fontaine of the London School of Economics says Pentecostal pastors sometimes identify children as witches, which leads directly to abuse. During the “curing” process, a child might fast for days, or be kept up for nights on end. One pastor says the praying involved can also be violent: people start “coughing out stuff”, he says, or fall on the floor. They may be cut. And simply being branded a witch means rejection and stigma.

So far in 2015 London’s police have been referred 60 cases of “belief-based ritual abuse” of children, up from 19 in all of 2012. They say such crimes are vastly underreported. Amma Anane-Agyei, who runs a council-funded service for African families in Tower Hamlets, an east London borough, says she is “overwhelmed” with a “frightening number” of cases. Terry Sharpe, from Project Violet, a police unit dedicated to the issue, predicts another big rise in these sorts of crimes next year.

This is not a problem in mainstream Pentecostal churches, says Elder Brown, a minister in Balham, south-west London, as most have strict child-protection policies (even, he says, the “ghostbuster” ones). Abuses are more often linked to the small churches that have sprung up in car parks and living rooms throughout Britain. These do not have many sources of income; curing witches, a service that can fetch up to £500 ($750), provides funds that help them compete for congregations, says a parishioner of the Universal Church of the Kingdom of God.

Police also worry about freelance exorcists, who belong to no faith and who advertise their wares freely: at Stratford station, on the edge of the Olympic Park, one hands out cards: £70 to get rid of demonic possession. (“It’s not right,” says a passing man. “You are cheating people.”)

Tackling abuses is difficult. Communities are closed, and pastors are powerful figures. “Police are scared stiff of being racist,” says Gary Foxcroft, who runs the Witchcraft and Human Rights Information Network, a victim-support group. Officers mostly rely on increasingly cash-strapped social services to refer cases. Victims seldom come forward, as they often wish to be “cured”. One boy, referred to Ms Anane-Agyei through social workers after he had been throwing himself against walls and talking about being taken to the cemetery to drink the blood of corpses, told her he was happy to die to save his siblings.

Abusers tend to be good at evading authorities, too. Some parents send their children to Africa for exorcisms (and some do not come back, says Professor La Fontaine). Small churches move from one borough to another if they feel they are under threat. Mr Foxcroft says that one Lancaster pastor who was caught helping child-traffickers is still preaching.

London police say they are raising awareness through educational films. Last year they worked with the Home Office to stop Helen Ukpabio, who preached that children who cried were servants of Satan, from entering Britain. Well established Pentecostal churches already report to the Charity Commission; fly-by-night pop-ups could do so too. Some have more radical ideas: Mr Foxcroft thinks pastors should be vetted by social services before being allowed to practise. As reported abuses rise, breaking the spell will not be easy.