Stephen Sondheim, musical theatre’s most influential composer-lyricist of the last half-century, was working on his most “virile and inventive” work yet at the time of his death on Friday. 

The writer behind such classic musicals as Sweeney Todd, Company and Into the Woods played songs from his unfinished latest project to West End producer and close friend Cameron Mackintosh just days before his death, Mackintosh has told The Telegraph.

Sondheim’s lawyer described his death as sudden.

On the evening of Sunday 21 November, Mackintosh spent an hour and a half on the phone with Sondheim “working through the score” of his new musical.

“He wanted me to listen to it and give him some feedback,” Mackintosh said.

The producer, who was responsible for the acclaimed 1987 London revival of Sondheim’s musical Follies, described the new work as “a very surreal piece”.

“There were some brilliant lyrics in it and some really good tunes. I kept saying: I like that, it would be good if you could extend this tune a bit more.”

Entitled Square One, the show was inspired by two films from the Spanish surrealist director Luis Buñuel: 1972’s The Discreet Charm of the Bourgeoisie and 1962’s The Exterminating Angel.

According to Mackintosh: “There were many things that only [Sondheim] would manage to make extraordinary.”

Restaurants, and food in general, are key themes in the new show, which made Mackintosh, with whom Sondheim frequently stayed when he was in London, “roar with laughter”.

“There is someone writing so brilliantly about food, and restaurant menus, and this is a man who can’t even boil an egg. He wasn’t very practical in that way.

Today at 7pm, West End theatres will dim their lights for two minutes in memory of Sondheim.