Its not a Brit musical, its a French one that has been translated into English.
Sorry, but it is a Brit musical - I should know - I was there on opening night at the Barbican Centre in London. The music was written by a French composer, lyrics were always in English. It starred Patti Lupone and dragged on for hours. I could not leave because Princess Margaret was drinking in the lobby (smart lady!) and security would not let us leave the building. It was produced by the Royal Shakespeare Company of Great Britain.