Hallelujah, Southwark! The London borough is home to the highest concentration of African-Christian churches outside the continent itself

Photographer Chloe Dewe Mathews has captured the transformation of her corner of the city, where an ever-increasing number of black-majority churches has sprung up in formerly industrial buildings, and gents in natty suits and women in elaborate headdresses walk to church through graffiti'd streets

A woman walks to church through the Copeland Park Industrial Estate in Peckham. There are said to be 11 churches, within this one industrial estate. (Chloe Dewe Mathews)

Having long lived around Camberwell and Peckham in south London, photographer Chloe Dewe Mathews has been used to seeing the transformation of her corner of the city on a Sunday morning.

With an ever-increasing number of black-majority churches springing up in formerly industrial or commercial buildings, the streets would buzz with church-goers – often dressed to the nines in Sunday best or traditional garb – making their way to worship.

Even so, she was struck to discover that Southwark has the greatest concentration of African-Christian churches anywhere outside the continent itself. She unearthed this seemingly unlikely fact from the University of Roehampton when researching the borough for a new commission from Tate Modern – for its "Tate Modern and You" outreach strand. That statistic – Southwark alone has over 240 African churches – was "so extraordinary" to Dewe Mathews, who is 31, that it became the spur she needed to pursue her own interest in the borough's religious life.

"I had a really open brief: [the Tate] said we want you to think about Southwark," explains Dewe Mathews. "Their new building is happening [a major extension due to open in 2016] – and are there other places or spaces in Southwark that are undergoing transformation in different ways? I live round there so it's particularly exciting – finding out more about a place you think you know. I've always been aware of that real transformation on Sundays, and of how all these ex-industrial spaces have been transformed into these religious spaces. But I just never knew it was to the extent that it is until I read that piece of research, and that made me feel this is something that's really relevant now – that scale is certainly noteworthy."

Dewe Mathews's project soon became a work of two halves: the contextual, the exterior, and then the personal, the interior. She documented the familiar pre-church scenes which had long caught her eye – gents in natty suits walking to church through graffiti'd streets, women in elaborate headdresses waiting for the bus – as well as the buildings themselves.

Despite using unassuming ex-industrial spaces, the black-majority churches often have the very grandest of names: Holy Ghost Zone, Freedom Centre International, Redemption House, Winners Temple, Life Changing International Ministry, Christ High Commission… "It's the contrast of these epic names with the mundane London exteriors which is quite intriguing and fascinating," says Dewe Mathews.

She also approached the pastors at several churches about documenting the services, and swiftly found herself welcomed into the fold, spending many Sundays getting to know a few congregations. The churches she visited were mostly Nigerian, although she also shot repeatedly at a Ugandan church. "I was welcomed, very much so. Often people were really open, really happy I was there – you might think because I'm different, that would be a problem, but it never was." She adds that while in, say, an Anglican church, someone taking pictures might be disruptive, within the African churches the set-up is less formal – services go on for several hours, people come and go more freely.

And many of them are making use of modern tech themselves. "A lot of the African churches already have a massive audio-visual set-up," explains Dewe Mathews. "They're constantly videoing everyone and projecting it back on k to a screen, like at a stadium gig or a football match – so people feel much more comfortable having a camera in that environment.

"It's also fascinating how different every space is – the churches service a certain community, a certain denomination from a certain African country. Some of them are extraordinarily like a club night: it's dark, there's dry ice, disco lights, an eight-piece band…"

The worship is typically exuberant, with singing, dancing, music, and an ecstatic prayer that may turn into speaking in tongues, as well as motivational sermons from the pastors. And the experience of attending these services had an unexpectedly profound impact on Dewe Mathews. "I feel confident in my lack of religiousness – I was brought up a Catholic, but it was quite a mild form of Christianity and I realised that it wasn't for me. So I thought when I went to these churches that I wouldn't be steered in any way. But there's something very intense about that amount of people outpouring their faith and emotion."

Witnessing this meant the project had to become about the inside as well the exterior – and Dewe Mathews captures the contrast of the anonymous grey London buildings and then the fervent, vibrant worship within. "It did become a dual interest – from an architectural point of view, how people have changed the spaces [into churches], but also what that very personal, spiritual experience is. And about the ways people act inside and outside: you get people wandering to church, having a chat, a real Sunday social ritual, and then once you get inside and the lights dim, it becomes a different part of yourself, the spiritual part. It's incredibly focused, and some people go into different states: it often ends up in speaking in tongues; it's very physical as well."

Normally, Dewe Mathews only takes photographs, but to attempt to capture that exuberant movement and powerful prayer, she felt she had to use film as well. A short film forms part of the exhibition at the Tate, while a multi-screen installation using her footage will be housed in an industrial space in the Peckham area in the autumn, bringing this local project back into the community from where it sprang.

'Tate Modern and You: Sunday Service' opens on Wednesday at Tate Modern, London (tate.org.uk)