Digital Spy sat down with Billy Connolly, who plays resident Wilf, and Sheridan Smith, the home's doctor Lucy Cogan, to discuss working on the Ronald Harwood-scripted film.
"I can't believe little old me is beside all that acting royalty!" said Smith, who shares several flirtatious scenes with Connolly's character.
She continued: "Billy's brilliant. He's good at ad-libbing, he can throw some extra things in. A lot of it was genuine laughter and flirting. He's got a little twinkle, Billy. I think Dr Cogan has a little soft spot for him even though he does overstep the line sometimes with his comments."
Connolly revealed that he occasionally grew tired of reeling off Wilf's double entendres, saying: "If that's all he had I would've pleaded to have him changed and rewritten. As it happens I've got Sissy (Pauline Collins) on my side to protect. She's getting a bit demented. It give it another edge, it was a joy to do."
Of the retired opera singers and musicians who were extras on set, Smith added: "When we weren't filming they'd all start jamming and Dustin would get on the piano.
"There was such a great atmosphere on set that a lot of the stuff in the film is genuine outtakes and laughter. It was all really spontaneous and magical, he's really captured that in the movie."
Quartet opens in UK cinemas on January 1.