Clarke Peters is being assaulted by five guys named Moe. One Moe slaps him on the head, another pushes him contemptuously, a third Moe pinches his nose. "They get all the laughs – I'm just getting tortured," he complains in his deep Barry White bass. Occasionally, he gives advice to a fellow cast member. "On that murder," he says, "it's moider." After half an hour of laughter and abuse, Peters decides to sit it out. "I'm too old to be doing this. This is a young man's game."

Peters, 58, is rehearsing at the Theatre Royal Stratford East for the revival of Five Guys Named Moe, the hit musical he wrote 20 years ago. For a long time, despite Five Guys, Peters remained relatively unknown. Then, after nearly four decades in the business, he found himself an overnight success as Lester Freamon in The Wire – the wise, intense detective who pays heavily for ruffling the feathers of Baltimore's power-brokers.

But as an actor, dancer, singer and writer, Peters has an impressively diverse CV. In the 1970s, he sang on hits such as Joan Armatrading's Love and Affection and Heatwave's Boogie Nights. In 1980, he appeared in the not-quite-so-classic David Essex movie Silver Dream Racer. Since then, he has starred in stage versions of Porgy and Bess and The Witches of Eastwick, and was virtually the only black face in Richard Curtis's Notting Hill.

And then there is Five Guys Named Moe. In the original production, Peters was one of the all-singing, all-dancing Moes; now he is the despairing Nomax, an older man than the character he first wrote, who knocks back the whisky and wonders how he lost his girl, until five guys named Moe emerge from his radio to cheer him up.

It's lunchtime, so we head off to the theatre's restaurant. Peters is an elegant man and moves so lightly his feet barely touch the ground. He orders baked potato and salad, and adds the tofu he's brought from home. Where did the idea for Five Guys come from? Himself, he says: he was Nomax. "I was in a wonderful relationship that was at a rocky point." My mutton curry arrives. "Bon appetit. I was working in Sheffield, and my house was down in the country, about five hours away, and I was driving down and Louis Jordan's lyrics seemed to be talking to me."

Was he wasting his life away? "Yes, I guess I was. We'd been in the relationship for some years and I just wasn't mature about it, and I wasn't treating her very nice." In what way? "It really was as simple as, if you make a promise keep it – what you might just say flippantly, someone else is taking very seriously. And they're building their plans and life around those promises. I'll be home for lunch, I'll be home for dinner, we'll be going away next week, small things that accumulate. Forgetting something like a birthday." Once he admitted his failings to himself, he says, the five guys started to come alive. "It was my therapy."

The musical's success saved Peters's relationship with his partner. It was their story, and they celebrated it together, but then their lives were torn apart. "We had a son who died," he says quietly. He looks past me, avoiding eye contact. "Guppy. That was the year Five Guys opened in New York, and it was such a momentous thing to go through that we lost sight of each other again." Guppy was four years old when he died of a kidney tumour. "You're so busy trying to fix your own grief that you don't know how to make space for someone else to go through it. It was very painful. Sometimes it still rocks my world." He asks if we can please move on.

Peters has two surviving children (the youngest, Maximillian, played little Michael Jackson in the West End production of Thriller). He lives with his wife Penny in London and has spent virtually his entire adult life in Britain. He grew up in New Jersey, and was politicised by the Vietnam war. One day, after attending a demo, he was arrested and locked in a cell with 12 others. Although a judge eventually cleared him of obstructing police lines, the experience scarred him. The protestors had been told they would only be arrested if they did not move on from the Ministry of Justice; they did, and they were still arrested. "It made me more angry than anything else, because what I experienced was how impotent you could be as an American citizen."

A tangle with the FBI

Soon after, in 1971, he followed his actor brother to France, to work on the musical Hair!. Was he a fully fledged hippy? "Most definitely. Especially the free love part. Not these days, though. It's not like it was." There was another reason for moving; while America was the home of celebrity, Europe was the place to learn your craft. (That has always been his motto: follow the craft.)

In France, he received a letter from the US government accusing him of evading the draft. "They were going to take away my passport, and my mother was really upset. I said, 'Ma, look, you know I haven't done that.' The last thing I was trying to do was hide, which is what my lawyer said when I was taken to New Jersey to stand before the FBI. I said to them, if the enemy comes to America, I'll be there, but I don't know the Vietnamese. If you put me in the army, I'm not going there. So yes, I was politicised after that, very much so."

Has America changed since his childhood? "Well, obviously, because we've got Obama in." Ah, Obama. I've got an important question to ask him. Obama loves The Wire, while David Cameron loves Holby City, another TV drama Peters has appeared in. Who has the better taste? He almost spits out his tofu. "You don't really want me to dignify that by answering! C'mon! How many people like Holby City here?" Well, Dave does. "I think you've answered your question." Does it say anything about Cameron?" I think it says a lot. Oh my God. How tacky is that?" Mind you, he says, Holby isn't that bad. "It paid for my mortage for a month, so I'd do it again."

Peters was born Peter Clarke; when he got to England in 1973, he discovered Equity was already oversubscribed with Peter Clarkes, so he did a quick flip. He worked with Ned Sherrin on a number of reviews, and this paved the way for Five Guys. "I asked Ned to help me. He said, 'We've done enough of these together, you can do it by yourself.'"

He followed up with Unforgettable, a musical about Nat King Cole. This time the reviews were shocking. "Unforgettable is, unfortunately, not the word," Jack Tinker wrote in the Daily Mail. Did the hostility affect him? "Well, you haven't seen me write anything after that, have you? I don't mind bad reviews as an actor, but when you put your creation up there, you still have an emotional attachment to it, man. The umbilical cord isn't quite cut yet." Did he decide not to write again? "No. I just haven't thought of anything more to write about . . . but maybe that was it."

There is a lovely, open quality to Peters. He talks eloquently about the sadnesses in his life. Almost 25 years ago, his brother had a terrible car accident. "He's still around, but he suffered brain damage. He was a good choreographer, and we had dreams of creating a musical theatre company. That will never be realised. But sometimes I know he's living it vicariously through me."

He has spent a good deal of time exploring different belief systems. He meditates, is a vegetarian, an advocate of tantric sex and and has gone through long periods of celibacy. Isn't the tantric sex a bit, you know, boring, just going on and on like Sting till you drop? He laughs. "I don't know, I don't have sex." Eh? But I thought you just said you were into tantric sex? Ah, that's the thing, he says: tantric sex is non-penetrative, and eventually involves orgasm, but not ejaculation. "You see, we think ejaculation is the male orgasm, but it's not. If you were to hold back your ejaculation, you would feel that energy begin to move through your body. It's beyond sex. We're a lot more than flesh and blood, you know. You think a man can have one orgasm and that's it, but if you're not overwhelmed by the moment of ejaculation, you can enjoy the moment time and time again. It's just as euphoric, but it takes time and you've got to have a partner who's willing and who you've got a special connection with."

The hugging conquests

When was the last time he had conventional sex? "I don't know . . . probably 13 years ago." Celibacy, he says, has enriched his relationship with women. "What I found was that I wasn't posing a threat to them, and I have more female friends. I found that I could really love and hug them without feeling, I've got a conquest here. When you're not burdened with that, there's a certain lightness to your life – my buttons aren't being pushed."

It's been a strange couple of years for Peters. The man who resisted stardom for so long has become an accidental star. He will soon start work on the second series of Treme, David Simon's follow-up to The Wire, and another microscopic portrait of a world rarely seen in TV drama (in this case, New Orleans after Hurricane Katrina). Peters shows me a photograph of the American-Indian he plays: swollen faced, clean shaven and big all over, he is unrecognisable. Lester Freamon was an expert at building doll's houses; this time Peters has mastered a new skill – beading. "I've got to live his life, and their tradition is to sew these magnificent suits for Mardi Gras."

He went back to America recently, and it reminded him how much he hates celebrity. "I see everybody chasing the money and forgetting about the stories. I see people not respecting the craft, but they become a commodity. You're just something on a shelf that the industry will take off, to give you some sort of formulaic adventure for their product."

Would he rather be where he is now, or back where he was when he wrote Five Guys? No contest, he says: now. "I had to go through those 20 years to get to where I am. Always be happy where you're at, mate, don't go backwards. I've been here this long, I've not killed myself, I'm not in jail, I'm enjoying a successful career. I must be doing something right."

• Five Guys Named Moe is at McEwan Hall, Edinburgh (underbelly.co.uk), until 29 August, then Theatre Royal Stratford East, London E15 (stratfordeast.com), 3 September-2 October.