Stephen Baldwin, 43, has 18 tattoos. "They represent various moments in my life," he says. "Whether it be showing my love for my woman in a very macho way – there are three of those – to the ones which express my commitment to sobriety. I have one for my children. The 3.30 one on the back of my neck is the time I'm supposed to be home! No, it's a scripture in the Bible that I feel compelled to remind myself of: John 3.30. "I must decrease so that he may increase." It's about consciousness of humility. I'm walking this walk and my life has nothing to do with my perception of the world. It's all God! How do I function within His plan?"

How, indeed? Nestled amid these lofty body adornments, at the top of Stephen's left shoulder, are two small letters: HM. They stand for… Hannah Montana. Miley Cyrus joked that she would get him a cameo in her Hannah Montana series if he got the tattoo and Stephen, a man who relishes a challenge, went straight out and did it.

"Hey, it's just one more," he shrugs. "And I have a beverage company that produces an energy shot, a Red Bull-type drink, called Hit Me. So I can say that the HM stands for Hit Me. Hit me! I'm fuelled on adrenaline with a chaser of the Holy Ghost! Yeeeeah!"

Stephen Baldwin is a character. Even his tattoos are bananas. The youngest and, some say, dumbest of the Baldwin brothers is a pumped-up ball of energy, a glitter-eyed alpha male, a charismatic Christian, a proper laugh. He charms everyone that wanders into his light. When he drops off his washing at a Camden launderette – "How are you all today, ladies?" – he has the manageress eating out of his hand. "Some of these nice jumpers we'll have to keep out of the tumble dryer," she offers; she has no idea who he is. But her young nephew, who's wearing a hoodie emblazoned with Playboy Mansion Security, is thrilled to see the Celebrity Big Brother star. Stephen beckons him over.

"Hey buddy," he stage whispers. "I've been to four of those Playboy parties. And you know what? They weren't so great." The lad flushes pink with excitement.

It's the Sunday after Stephen's Friday-night eviction from the Big Brother house. He's not had much sleep since: after the show, he went out with Sisqo, his fellow evictee, to Old Compton Street tourist trap Balans, of all places, where they hooked up with CBB ex-housemates Lady Sovereign and Kat. Then, last night, he trekked to an internet cafe at 3am so he could co-host his religious radio programme, Baldwin/McCullough Xtreme Radio, which goes out live every Saturday evening to 195 stations across the US. He didn't go to sleep until six in the morning.

Still, there's not much evidence of tiredness when we meet, in the restaurant of his hotel. It's nearly noon and Stephen is running late for his appearance on Big Brother's Little Brother. He avails himself of the breakfast buffet at a leisurely pace. "The car they've sent has a flat tyre," says the PR, "so we're OK for a few minutes." Stephen says: "See this? This is MOR-TA-DEL-LA. We need to make time for this."

There is an enormous Bible on the table. Stephen takes it everywhere; he specified in his Big Brother contract that he be allowed to read it for an hour a day while in the house, despite there usually being a blanket ban on reading material.

"I ain't going in the House of Hell without my sword!" he trumpets. "I only look stupid… And there wasn't much to do, so guess what? The Bible readings became a big thing! I'm like, 'Wait a minute: I'm not holding a Bible study class while the whole world watches, am I?' I spoke with everyone about God, except for Vinnie."

Actually, Stephen – Stevie B, as he refers to himself – is convinced that he saw the devil while he was in Big Brother, working from within two of the housemates. (He won't tell me which, though I'd guess at mild Nicola T and dimbo Dane Bowers, both remarkably undemonic.) Whatever, the devil popped up and Stevie B spotted the ­little rascal.

"Demons manifest themselves in people in different ways," he says seriously. "For instance, out of nowhere, somebody can become very angry for no ­reason. That's not just an emotion. That's a demon."

Stephen tried to talk about this with other housemates, but they didn't seem that bothered that some of their members were possessed. So he consulted with God, and came to this conclusion: the Holy Spirit is allowing Stephen to see certain things… "BUT! If I mentioned it, it would destroy my credibility in the house. Satan would be using my knowledge that he exists against me! I can't reveal the truth! This," muses Stephen, "is gnarly warfare."

"Give me 120 seconds," he says to the PR and nips over to talk to two British people that he met in the hotel lobby yesterday. They're from Yorkshire and invite him to accompany them to see Leeds replay Tottenham in the FA Cup in a few days' time. "Sure!" says Stephen. He has spoken, and so it shall be.

We take a cab to the Big Brother house, in Elstree. On the way, Stephen talks about his family. Born in a small town on Long Island, New York, he's one of six children – two girls, Elizabeth and Jane, and four now-famous boys: Alec, Billy, Danny, Stephen. Their Catholic parents were respected community members – his dad was a schoolteacher, his mum founded a breast cancer care centre – and the Baldwin brothers were popular: "Badly behaved, outspoken, famous-in-our-town, dumb jocks." Stephen was the baby, his mum's favourite: "Like Michael Jackson in the Jackson 5 years, with confidence in my charm and a belief in my ability to be entertaining."

Alec, then and now the leader of the Baldwins, became president of his school's student body, followed by Billy and Jane. He studied acting at NYU and, in 1980, Alec got a role in a daytime soap called The ­Doctors. The other boys ­followed, landing modelling and acting jobs through, says Stephen, "chutzpah, personality, drive and a belief that anything's achievable". Everything came easily to the confident ­Baldwin ­brothers.

Up until he found the Lord, Stephen worked pretty solidly as an actor, his ­biggest roles being in mid-90s ­movies The Usual Suspects and Bio-Dome; though he nearly blew his career early on, by getting heavily involved with ­alcohol and cocaine. He first took coke at his high school prom. But he was clean and out of rehab by the age of 23, having met his Brazilian wife, Kennya, when he was 19. They married in 1990 and have two girls, Alaia, who's just turned 17, and Hailey, 13.

Kennya has been instrumental in Stephen's conversion from Catholicism to born-again Christian. When Alaia was first born, Kennya hired a Brazilian woman, Augusta, as a housekeeper. As she worked, Augusta kept singing about Jesus and Kennya asked why: Augusta replied that her local church in Brazil had told her that she should take the job with the Baldwins because, if she did, they would become believers and have their own ministry. Kennya told Stephen. He laughed.

Some time later, Kennya became born again. "I gave my life to the Lord tonight, she said," remembers Stephen. "I said, 'That's awesome.'" But it involved more than he expected: every day Kennya would get up and pray silently for two hours, her face pressed to the floor. She did the same thing every night, as well as study her Bible for 45 ­minutes. After around nine months, Stephen joined in, though he didn't really feel the force until 9/11 and the collapse of the Twin Towers.

"I live in New York. And I thought, 'What's up with that?' It was the prophetic, supernatural, spiritual impact of 9/11. Something shifting for no logical reason – well, then, Jesus Christ could come back for real. Things are no longer as they were before. Now the impossible is possible. And if the impossible is possible, and a woman came and told my wife that we would lead a ministry…"

Stephen was convinced that 9/11 was a sign from the Lord. Which it may have been, though it's hard to believe that God caused all that tragedy just to inform one fairly successful actor that he should jack in his career and start skateboarding for Jesus. But anyway, Stephen set up a company called Global Breakthrough Ministry and staged a very popular arena tour around the US, which mixed extreme sports and evangelism. A spin-off video called Livin It, which he directed, has gone on to sell 500,000 copies.

Opportunities kept coming: he did a tour of churches, hooked up with Kevin McCullough and started his radio show, wrote two books, set up an outreach service to help members of the US armed forces. Over the past few years, however, he says he's tried to calm down and listen to the Lord more – and this, weirdly, has led him to do a series of reality shows in the US, including I'm a Celebrity… Get Me Out of Here, which he hated, and Celebrity Bull Riding Challenge, which he enjoyed.

We arrive at the Big Brother studio, where Sisqo and Stephen partake gamely in BBLB, with George Lamb taking the mickey out of them throughout. Both Americans are great performers; funny, reactive, quick to get the joke. "Do I love bootleg jeans? Sure I do," booms Stephen, and flips up his trouser hem to reveal his iPhone tucked into his sock. "I'm from New York! It's a great place to hide a small 38 revolver!"

Stephen got £150,000 for the show. Which sounds a lot, but he went bankrupt last year, owing $824,488.36 in unpaid mortgage and an unspecified amount, believed to be over $2m, to the IRS: "I didn't plan for a rainy day. I didn't know the Jesus freak thing was on the horizon!" A casting director told him recently that he'd been put up for three different films, but each time, the director said no, specifically because Stephen can't keep quiet about his faith. Anyway, he tells me, he can't do the films he used to, because of the gratuitous violence, bad language and sex. If he were offered The Usual Suspects today – which is unlikely – he would have to say no.

Off we go again, this time to Nigel Hall on Floral Street, where a stylist whizzes Stephen in and out of some nice clothes. (He can't be that skint: the discount comes to over £1,500.) Stephen is a laugh throughout. "Take a picture!" he says, and organises it so he's in the best light. "My wife will rape me in this outfit. Rape. Me." He keeps ­telling me not to quote him when he uses what he thinks is louche language, such as "balls": being a Christian, for him as for many Americans, means he has to stick to a rigidly conservative agenda. It impacts directly on his life: his father-in-law, who divorced Kennya's mum nine years ago, is not allowed in Stephen's house with his girlfriend. It would be OK if they were married, but until that happens, "until he is acting in a way we feel acceptable according to our faith", then no.

Our final stop is a small shop in ­Kensington, where a service for the Every Nation Church is being held. Earnest, smiley young people sit on cushions to hear their pastor speak. They sit a lot longer for Stephen's talk: once he starts, he can't stop, telling them the story of his conversion, dragging it out for giggles, relishing his chance to speak freely about his faith without Vinnie Jones butting in. It's 45 minutes of fun. Stephen is a remarkably likable man, I think.

But then, the day after, we speak again on the phone and I ask him what he'd do if one of his girls came out as a lesbian and the other became a stripper. "Jesus or no Jesus, if my kid started working in a strip club, I'd beat her ass," he hoots. "Now, the other question is interesting and culturally relevant. I have two or three very dear friends who are homosexual and they know I'm born again and we have an understanding that we're just not going there…"

I'm not surprised. For the next 20 minutes, we have an intense discussion – argument, really – during which Stephen reveals that he's all for gay men who, through their faith, reject their homosexuality and get married: "To turn away from that lifestyle is astonishing." Yes, Stephen, it is. And he's definitely not for gay marriage.

What about civil partnerships, I ask wearily.

"I believe that the family unit has fundamentally been the most positive thing for society and I don't believe that any minority has the right to create changes that impact on the majority. That's really the only issue for me."

And so Stephen and I part company, both feeling disappointed in each other. It's a shame, but it's one of those things. You can really like someone, but when you disagree so decisively on the way you should treat others, you can never really be friends. Honestly, what is it about American born-again Christians that makes them so intolerant? ­Whatever happened to loving thy ­neighbour?