Hoffman makes debut in a lyrical ode to growing old and mortality

"Billy's sounds the best," adds Collins, the 72-year-old actress who remains best known for the hit stage play and subsequent screen adaptation of Shirley Valentine, "because it's got his Scottish accent struggling to get out".

Hoffman's film is an adaptation by Ronald Harwood of his 1999 play about life at Beecham House, a fictional country retirement home for British musicians and singers, where the virtues of a life spent dedicated to the creative arts are balanced by the struggles of old age and the ever-present whispers of mortality.

Quartet suggests that even in retirement, these performers play the parts they believe they should. For Collins' character, Cissy, that means keeping up a sunny exterior while trying to deal with the first signs of dementia familiar banter with Connolly's typically roguish Wilf is a way of fixing herself in a familiar, reassuring place.

"She's very good at concealing it, as many dementia sufferers are," Collins says. "But it's also a joyful film.

"The important thing is not stopping doing what you love to do. That's what gives you your energy. I don't want to work non-stop, but doing a role refreshes your mind and stops you being lazy."

Collins credits Harwood, whose other stage credits include The Dresser, as well as the Academy Award-winning screenplay for Roman Polanski's The Pianist, with a "great ear" for dialogue. In updating the text, which received mixed reviews on its West End debut, Harwood has literally opened up the piece for Hoffman, introducing a raft of supporting characters and grounds for the camera to explore.

Those playing the additions include the great Michael Gambon (Harry Potter's latter-day Professor Albus Dumbledore), whose retired but still dictatorial director stages an annual fund-raising concert for the facility. When Smith's Jean arrives at the home, Gambon's character hits on the idea of reviving the third act of a revered production of Verdi's Rigoletto, featuring the four leads, even though Jean's marriage to Courtenay's Reginald ended badly and they have not spoken in decades.

Like the characters they play, the four lead actors have their own shared history and mutual friends, some now departed. Collins says that she has always got on well with Maggie Smith because they were never rivals: Collins, a lifelong Londoner, tended to play working- and middle-class parts, while Smith - who has made aristocratic sniping an art form on television's Downton Abbey - naturally gravitated to the upper-class roles.

"I'd be cast as her maid," jokes Collins, and it was Smith and Courtenay who suggested Collins for the role of Cissy to Hoffman, who hired her after watching Woody Allen's You Will Meet a Tall Dark Stranger and spending two hours on the phone in an introductory trans-Atlantic conversation.

"My dearest wish is that he wins an award for best debut director, as it would be very funny given his age," notes Collins of the 75-year-old Hoffman. "He's very emotional, very gentle with actors, and also if you say to him, 'I don't think this is working', Dustin will actually say, 'I'm sorry, I was wrong'. That is very rare for a director."

The crowd-pleasing Quartet is seen as part of a wave of features that reflect the concerns of an ageing audience who want to see stories - and actors - who reflect their own station in life. The template is John Madden's recent success The Best Exotic Marigold Hotel, which also starred Smith, and Collins would like to see further instances.

"It's happening, but we could do with it happening more. I loved Best Exotic because the characters were taking a brave step at an unexpected age," she explains. "And hopefully younger audiences will come as well because they might recognise their grandparents and realise that rather than knitting something, grandma might like to go out skateboarding."

Quartet opens on December 26.