At least six people have died in Britain after being told that they had been healed of HIV, and could stop taking their medication.
There is evidence that evangelical churches in London, Manchester, Birmingham and Glasgow are claiming to cure HIV through God.
We sent three undercover reporters into the Synagogue Church of All Nations (SCOAN) , which is based in Southwark, south London.
All of them told the pastors that they were HIV positive. All were told that they could be healed.
Once a month the church has a prayer line, where people from across Europe come to be cured of all kinds of illness.
At registration they have to hand over a doctor's letter as evidence of their condition
The healing process involves the pastor shouting, over the person being healed, for the devil to come out of their body, and spraying water in their face.
One of the pastors, Rachel Holmes, told our reporter, Shatila, who is a genuine HIV sufferer, they had a 100% success rate.
"We have many people that contract HIV. All are healed."
She said if symptoms such as vomiting or diarrhoea persist, it is actually a sign of the virus leaving the body.
"We've had people come back before saying 'Oh I'm not healed. The diarrhoea I had when I had HIV, I've got it again.' I have to stop them and say 'no, please, you are free.'"
SCOAN told our reporters they would be able to discard their medication after their healing and that they would be free to start a family.
Former health secretary Lord Fowler, who led the HIV/Aids awareness drive in the 1980s, says this message is dangerous.
"It is foolish advice and it is tragic advice because the consequences of this kind of advice can only be that people pass on HIV and can only be seriously bad for the individual concerned - including death."
Medical professionals have told Sky News of at least six patients who have died after being told by various churches to stop taking their HIV tablets.
Emmanuel came off his medication a year ago, on the instructions of a pastor at his church in North London.
"He told me I'd been healed: 'You've got to stop taking the medicine now. I'll keep praying for you. Once God forgives you then the disease will definitely go.'"
Emmanuel admits he suspects he may have passed his HIV onto his boyfriend.
"Yeah, I think I've passed it on. He got ill. Physically he's lost some bit of weight. He's very small. I think he's worried... Yeah I feel guilty, if I'm the one who passed it onto him I'm feeling guilty. Yeah very much guilty."
The Synagogue Church of All Nations is wealthy. It has branches across the globe and its own TV channel.
On its website it promotes its anointing water, which is used during the healing, and it also makes money from merchandise, such as DVDs, CDs and books.
Church members are expected to give regular donations.
It is also a registered UK charity. The Charity Commission is looking at our findings.
The Department of Health says it is very concerned: "Our advice is clear that faith and prayer are not a substitute for any form of treatment, especially for HIV treatment."
Sky News asked the church for its response to our investigation. Here is its statement:
"We are not the Healer; God is the Healer. Never a sickness God cannot heal. Never a disease God cannot cure. Never a burden God cannot bear. Never a problem God cannot solve.
"To His power, nothing is impossible. We have not done anything to bring about healing, deliverance or prosperity. If somebody is healed, it is God who heals.
"We must have a genuine desire if we come to God. We are not in position to question anybody's genuine desire. Only God knows if one comes with true desire. Only God can determine this.
"That is why, if anybody comes in the name of God, we pray for them. The outcome of the prayer will determine if they come genuinely or not."