There is an element of the Christian faith in the UK that is trying to buck the long-term trend of decline in the number of followers.
Most congregations in the country have seen a steady drop over recent decades.
But one course that teaches the basics of Christianity - selling itself as a chance to "explore the meaning of life" - has enjoyed a resurgence.
The course originated in an Anglican church in London's Knightsbridge more than 20 years ago.
There are now some 30,000 Alpha courses running around the world, say organisers. Sessions are held in prisons, workplaces, schools, colleges and military establishments.
Around 7,000 UK churches are signed up, many running several courses a year.
The number of converts does not match the tide of Christians leaving the church, says Alpha communications director Mark Elsdon-Dew.
Critics
But Alpha predominantly attracts young people - aged 27 on average - a good sign for the future, he suggests.
A 'supper' held at Holy Trinity Brompton (HTB) church - the home of Alpha - marks the end of the latest 10-week course.
I am welcomed with beaming smiles and enthusiastic handshakes, and sat at a table of 10 tucking into salmon, couscous and wine.
Alpha has been praised by church leaders and boasts celebrity endorsements.
But it has also attracted criticism as a "Coca Cola" version of Christianity, over the way it is marketed.
Some say Alpha is more a rich social club than a Christian coming-together. Others are uncomfortable with what they call its prescriptive teaching and attitudes towards homosexuality and other faiths.
'What made you come here?' I ask 'graduate' Abigail, 30, who tells me she was the "rebel" in a Christian family until recently.
It's a complex tale, involving a break-up with a boyfriend and the disappearance of a benign cyst in her eye following a prayer to God.
Alpha male
Soon after she moved in with her sister, who is married to a curate at HTB, got a job there and became involved.
"Everything has fallen into place. Before I said I was happy, doing my own thing. I thought Christianity was fine for my family but not me.
"But after I said the prayer in the second week of the course that was it."
Another woman says she was already a Christian but felt there was something missing.
She breaks down while describing the Holy Spirit weekend - a part of the course which involves, in the words of one course-goer "experiencing the love of God directly".
"I feel like a whole person for the first time. And all because I found God."
Not all are convinced. One man said: "It was interesting but I don't feel I have been successful in building a relationship with God."
There's a collective groan as he admits he did not attend the away weekend, which many see as a crucial.
But he is applauded when he adds: "I'll do it in November and we'll see what happens."
Nicky Gumbel, Alpha's creator in its present form, spreads the message in person or via videos around the world. The Alpha male, so to speak.
He says Alpha is growing because there's a "spiritual hunger in every heart".
"It's hard to find a place in the modern world where you can discuss it in an unthreatening environment, where there are people just like you. People tell friends and it grows.
Clubs and drugs
"You see how it changes people's lives. We want the divorce rate down, crime down, the prison population reduced. Politicians can only change certain things. They can't change people's hearts."
Talking of crime, ex-Metropolitan Police officer Simon Pinchbeck, 47, is less typical of the wealthy set HTB has a reputation for attracting.
On day one I nearly walked out - it was the enforced happiness and guitar playing
Pete Davies
At 40, he says, his life spiralled out of control. He started clubbing, taking drugs and left his family.
"I got pensioned off from the police. I was bitter. I got into the wrong crowd and turned to making a living out of crime.
"Then God sent me a lifeline. There was a guy in the gym, a violent drugs baron, who had turned his life around through faith. He looked so peaceful. I said I've got to have some of what he's got.
"Coming here was like nothing I've ever experienced. The feeling when the spirit of God entered my life was unbelievable."
'Alpha's Tony Blair'
Alpha staff are the first to admit its style is not for everyone. Pete Davies - a management consultant who asked that his name be changed - would agree.
"On day one I nearly walked out - it was the enforced happiness and guitar playing. There was something sickly about it."
He describes Nicky as the "Tony Blair of the Alpha world" - a polished speaker with some "Mandelson-esque sidekicks".
"Gradually you are sucked in to this well put together argument."
He said Alpha at HTB came across as a "champagne religion" that was not socially inclusive.
"Also it's not hugely tolerant of other religions which is quite pertinent in this day and age."
Despite this he still thinks the experience was worth exploring, describing the weekend away as "deeply moving".
"There was definitely something going on. But did I find the Holy Spirit? Probably not."