"New" is not quite right. Bart wrote the words and music for Quasimodo, based on Victor Hugo's 1831 novel Notre Dame de Paris (The Hunchback of Notre Dame) in 1963, or 1964 - he can't quite remember. The poignant tale, set in 15th-century Paris, of the love between the deformed bellringer and the beautiful gypsy girl Esmerelda nearly made it to Broadway, where it would undoubtedly have joined the list of Bart's stage hits: Lock Up Your Daughters, Fings Ain't Wot They Used t'Be, Oliver!, Blitz! and Maggie May. But there was a complicated wrangle about who was to direct the show, and it was put on ice.
Then there followed one of the gloomiest cliches in entertainment - 20 years of drink and drugs. But, now 65, Bart is back, booze banished, life straightened out, driving on a cast drawn from veterans of the hit musicals of the past decade: Starlight Express, Miss Saigon, Les Miserables, Jesus Christ Superstar, and Ain't Misbehavin'. A couple of minutes' walk from the London Palladium, where the revival of Oliver! is playing to full houses, he is hard at work getting Quasimodo ready for a private performance in front of anaudience of impresarios, producers and critics on 22 November, starring Ray Shelland Frances Ruffelle.
Bart says: "I've been fascinated by this story since I saw Charles Laughton as the hunchback in the 1939 film version. I was inspired by the story of this marvellous soul within a monstrous body. The simple premise of the piece, when I wrote it, was the question, 'What is ugly?' I hoped that you could realise, when you left the theatre, that the guy at the end of the row wasn't so ugly after all.
"But things dragged on ... it never got made. Since then I've looked again at the original. In his story the hunchback was only 18 - not Charles Laughton at all. Esmerelda was only 16, a street kid. With the obsession of the priest, Frollo, who is the hunchback's mentor, it suddenly came together as an involved, modern, dark subject."
Bart's decline began with Twang, a musical about the life of Robin Hood, in 1965. It seemed like a good idea at the time. He smiles at the memory of "my famous flop". The critics panned it, the public stayed away.
That's showbiz. He was only 30. But by the end of the 1960s, Bart, who had started his musical career in Soho with Tommy Steele in the mid- Fifties, had had a surfeit of showbiz. He had emerged for a time as one of the world's most successful composers and lyricists, the Andrew Lloyd Webber of his day. He partied with the Beatles and the Stones. He was romantically linked with the singers Judy Garland and Alma Cogan.
As the Sixties died, so did his friends: Cogan, Garland, and Brian Epstein, the Beatles' manager, were all gone. There was another musical flop - La Strada, in 1969 - then next to nothing for 20 years as Bart grappled with the bottle and other related demons. But now, with Quasimodo, there is renewal, and hope. "Doing this is for me. It's to get my juices going again, which it has, I'm pleased to say. I've had a long break from new work. It has been so long that it's a bit like looking at someone else's work. I have to look at that kid who was writing 30 years ago and say where is my head now in 1995?
"Surprisingly, a lot of it still works. I remember when I'd written some of the music and lyrics I sent the script to Noel Coward. He said: 'Brilliant, dear boy, but were you on drugs when you wrote it? It seems a little bit abstract here and there.' I suppose it was. It's good to look back through that haze with a new clarity."
London-based American actor Ray Shell was pleasantly surprised when he got the lead role in the workshop. "Les Mis doesn't have any black folks in it at all," he says. "I feared this would be the same.
"I didn't want to do it at first. It's about being someone that other people find ugly and repulsive and what that does to your confidence and emotions. It's about how difficult it is to know someone else's soul. Despite his physical ugliness Quasimodo has a child's heart and mind. We're all Quasimodos in a way - people judge us by the way we look, not how we are inside."
Bart says: "It's a tragic story, but about being free to change, free to renew oneself. In a way I became the hunchback. It's a great release and a catharsis for me to put it all in this work."
By now he is looking distracted. It's 4.30 on Friday afternoon, the cast want their weekend, but there is a scene to get right. There are 10 days to go before the money men come to cast their cold eyes on a show that has already been more than 30 years in the making.
If they give it the OK, it may get on the West End stage in 1997. Maybe. Lionel Bart has the look of a man who is in a hurry to make up lost time.