It seems fitting that the man who wrote the words for musical extravaganzas such as Les Misérables and Miss Saigon should have a dramatic home, but when an estate agent tried to persuade Alain Boublil to take a look at St Saviour’s, a huge converted church in west London, he thought he was mad. “I refused to visit it three or four times,” he says in the heavy French drawl he has retained despite having been based in London for more than a decade. “Then, one day, I was walking past it and had a look inside. After five minutes, I knew I wanted to live there.”

And boy, has he lived in it. Since Boublil, 68, moved in with his glamorous French wife, the singer Marie Zamora — they met in 1991, when she was playing Cosette in his Paris production of Les Mis — the former church has been the setting for private concerts, birthdays and theatre workshops, with Zamora singing and playing the piano for dozens of guests.

“The acoustic is extraordinary,” he says. “Guests couldn’t believe their eyes. Some were a little overwhelmed. But after 15 minutes, many would say they felt as if they had been there before.” To Sunday service, perhaps.

Six years on, Boublil, Zamora and their two sons, Adrien, 14, and Maxime, 13, are relocating to New York — and they’re selling up. The five-bedroom, 8,600 sq ft property is on the market for £15m — ambitious, perhaps, given that he bought it for £8.25m in 2003 and has done little work to it since.

The Tunisian-born librettist began his career by producing La Révolution Française, which was the first French rock opera when it opened in Paris in 1973 — the first of many collaborations with the composer Claude-Michel Schönberg. The pair are best known for Les Misérables and Miss Saigon, which, between them, have been seen by more than 83m people worldwide; Les Mis has been performed in 38 countries.

Boublil was back in the spotlight earlier this year after Susan Boyle’s performance of the Les Mis show-stopper I Dreamed a Dream on Britain’s Got Talent. “You couldn’t avoid it — the American media went mad for her, and I was called in to speak about it on chat shows and news channels,” he says. Not that he is complaining: “She has given the song a great new popularity. She is like a modern Edith Piaf — untrained, and she has come from the street.”

Grade II-listed St Saviour’s was built in the late 19th century, is the only Church of England church in central London to be converted into a single home rather than flats, which explains the price tag. “There are plenty in the country, but they tend to be smaller — chapels rather than churches,” says Jonathan Hewlett, head of prime London homes for Savills estate agency.

The church became derelict in the mid-1990s and could no longer be maintained, so the congregation moved to a hall next door, and a developer, the Raven Group, bought the building and set about converting it into a home.

The original external structure has been retained — as have many of the original features, including stained glass windows, column details and eight carved stone angel heads that hold up the beams in the ceiling. But wouldn’t it feel blasphemous to live there?

Not for Boublil. “It has been very fruitful for me — a good place to work in,” he says. In fact, once he moved in, the religious connotations didn’t even cross his mind. “I never thought of it as a church, maybe because it’s not my religion. Not everyone could do it, though. You have to be in sync with the house.”

The building was gutted and completely rebuilt inside: the most dramatic feature is a mezzanine-level living room with wooden beams and 60ft ceilings, reached by a grand curved staircase. The master bedroom leads off it; there is another guest bedroom on that floor, with two more for the children on the two floors above. The basement was gutted and turned into a pool, sauna and steam-room complex. Although there is only a tiny garden, the property does have a roof terrace.

“It’s impressive and cosy,” Boublil says. “It is not grand. Its luxury is in its shape, its volume and its inspiration.” Indeed, the plain cream carpets, painted walls and light-wood finishings give a rustic look — there is not a luxury item or high-tech gizmo in sight.

Boublil’s favourite part of the house is the dining room, on the left as you go in. “I had all the projects I was working on spread out in different parts of the big table,” he says. The room is also home to the trinkets he has accumulated throughout his life: a hand-made wooden ship he picked up in Mauritius 30 years ago, and a model helicopter made from old Coca-Cola cans, a joke Miss Saigon present from David Hersey, the lighting designer who worked with him on the musical.

Elsewhere in the house are the first-edition Victor Hugo tomes given to Boublil by Cameron Mackintosh, producer of the first English-language version of Les Misérables — one of many adaptations of the French classic.

Because of his theatrical background, Boublil has paid a lot of attention to lighting — and the church is decked out with unusual and striking lamps. “I love modern chandeliers. As in the theatre, they are crucial — the way you light a show makes all the difference and can change the audience’s mood.

“There are corners of the house where the lighting is arranged in such a way that you are only aware of the area you are in,” he says. “You can get an intimate setting.”

Boublil says that he would be sad to see the house standing empty (and probably even sadder not to get his £15m). Who does he see living in it?

“It’s for people with an artistic mind, who can create in it,” he says. “It’s also a house for someone who likes to stay at home and who can take the time to explore it properly — every corner has a story.”

St Saviour’s is for sale through Charles McDowell; 020 7581 8357

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