“With films, of course you’re filming one every two years or so, so filming four [would mean] they’re going to be eight years older than they were on film one.

“So the Hollywood thing, by and large, is that you get people you can age up a little bit. They might have people in their 50s and 60s playing people in their 70s. I think that’s the tactic. I don’t know who they’re going to have, by the way, but they might go a little bit younger and do a little bit of a make-up job.”

Osman said other reader suggestions for the four main characters, besides Dame Helen, 76, are Dame Penelope Wilton, 75, and Kenneth Cranham, 76.

The author’s mother, Brenda, whose own home in a retirement village inspired the novels, has suggested Imelda Staunton, 65, and Celia Imrie, 69.

Appearing at the Cheltenham Literature Festival, Osman, who combines his writing career with hosting the television shows Pointless and House of Games, said that the age of the protagonists was important to the story.