A new religion is spreading to Britain - its central sacrament the consumption of a hallucinogenic Class A drug. Here's a report from the faith's heartland in the rainforests of the Amazon

I am deep in the Amazon rainforest, anxiously losing my mind as the world begins to disintegrate. Around me, all sense of distance is wrapping itself up like spatial origami, slowly shrinking until an entire dimension has disappeared. A moment ago, I was surrounded by 200 people dressed in white and singing like angels, but now they occupy the same space as me... if that makes any sense.

Wherever I look, that is where I am. I can see everything from every angle, all at the same time. In fact, I feel I am everywhere. Outside, in the forest, the thrum of frogs and cicadas drowns out the sound of shrieking monkeys. Below me, the floor is shimmering, vanishing in waves like a spent mirage. Behind, I feel a cold vibration on my neck and sense a growling malevolence. I turn and see a red door, bulging at the hinges. Overcome with dread, I push hard to keep it closed, and all the while I feel a horrible nausea.

When will this end, I am thinking. And, with sweat running down my forehead, how can I survive it? Welcome to the Church of Santo Daime, one of the fastest growing religions in the world. Its mixture of Christianity, South American shamanism and African animism is proving irresistible to thousands of new believers across the globe. But it is its central sacrament, ayahuasca, a powerful hallucinogenic brew made from rainforest plants - a brew that I have just drunk - that makes the Church so appealing to some yet so controversial to others.

Santo Daime groups believe that ayahuasca, or Daime, as they call it, is a manifestation of Jesus Christ that brings them closer to God. Their visions, sometimes terrifying, sometimes blissful, help them to make sense of themselves, their universe and their god. Theirs is a young church - less than 80 years old - but in recent times it has spread throughout South America to the US and Canada, the Far East and Australasia, across mainland Europe and on to the UK.

According to followers I have interviewed, the number of worshippers in Britain is in the mid-hundreds, operating in London, Devon, Cornwall, Northern Ireland, Wales and Yorkshire. But these numbers are growing in spite of an obvious hurdle - the active ingredient in ayahuasca, dimethyltryptamine (DMT), is a Class A drug.

British Santo Daime groups meet secretly, always, as one put it, “afraid of the knock on the door” because of their (as yet untested) legal status. They worship in each other's homes, community centres, colleges and church halls, often telling landlords that they need them for choir practice. They never advertise and new members are allowed to attend strictly by invitation only. But among those in search of spiritual enlightenment - among weekend New-Agers too - the word is spreading; followers of Santo Daime claim that one session with ayahuasca is worth 100 hours of therapy.

If you don't have an invitation, then, but you want to attend Daimistas' worship, understand their beliefs and drink their sacrament, you might have to do what Domenico Pugliese (a photographer) and I did: travel 8,000 miles by plane, bus and boat to Céu do Mapiá, deep in the Amazon. This is Santo Daime's very own Shangri-la, a community of some 700 people living out their dream in the rainforest. Because here, as across all Brazil, the use of ayahuasca in a religious context is perfectly legal, treated even with deference by academics, politicians, medical researchers and theologians.

The Church of Santo Daime (“holy give me” in Portuguese) was born in the 1930s out of the experiences of a Brazilian rubber-tapper named Raimundo Irineu Serra, or Mestre (Master) Irineu, as followers call him. He was born in 1892 to African parents in Maranhão in the northeast of Brazil and travelled to Acre in the northwest in 1912 to find work during a boom time for the rubber industry. In 1930 he was given his first taste of ayahuasca by indigenous shamans - medicine men - and spent eight solitary days and nights in the rainforest, experiencing a series of visions and receiving instructions from the Virgin Mary, whom he called the Forest Queen, that formed the basis of a new religion.

It was predominantly Christian with an emphasis on nature - on the spirits of the rainforest - and it espoused spiritual growth through the drinking of ayahuasca during carefully defined rituals. In subsequent years Mestre Irineu shared his teachings, experiences and ayahuasca with growing numbers of fellow rubber extractors before building his own church, Alto Santo, on the outskirts of Rio Branco in Acre.

After the death of Mestre Irineu in 1971, the church split into various factions. The most important - which moved to Céu do Mapiá in the early 1980s - was led by one of Mestre Irineu's closest disciples, Sebastião Mota de Melo, or Padrinho (Father) Sebastião. It is this branch of the Church, also known as CEFLURIS (the Eclectic Centre of the Universal Flowing Light of Raimundo Irineu Serra), which is spreading fastest today.