After running for six seasons over 21 years, from 1992 to 2013, the classic British sitcom Absolutely Fabulous arrives on the big screen in a flurry of champagne and cameos. Originally a short sketch on the French & Saunders show, the enduring characters have had a rather patchy ride, with some episodes funnier than others.

Benedict Cumberbatch at a Q&A with US President Barack Obama at London's Lindley Hall.

It was a year and a half ago that writer-star Jennifer Saunders was challenged by Dawn French to make the movie. "We were doing our New Year's show on Radio 2", Saunders says, "And Dawn said, 'What are you doing in the next year?' I said, 'I'm going to write the Ab Fab film.' She said, 'Alright. And if you don't, you have to pay me ten thousand pounds!' And I said, 'Okay.' It was the greatest incentive I ever had. I probably wouldn't have done it without that bet."

The movie hinges on Saunders' Edina and Joanna Lumley's Patsy accidentally knocking Kate Moss off a balcony at a showbiz party. "I had written it and almost sold the film when someone asked, 'Have you asked Kate?'" Saunders says. "I just imagined she'd say yes. So I felt really nervous sending her the script. I got a text back saying, 'Love it!' That's all you get from Kate."

And that was only the first of the film's myriad of cameo appearances, from Jon Hamm to Joan Collins. "The truth is, we needed people for party scenes and red carpet and even for the news reporters," Saunders says. "I don't think anyone said no. But lots of people weren't available. We wanted Benedict Cumberbatch."

Lumley picks up the story: "I went to see him in Hamlet, went backstage to see Ben and he said, 'I'm gonna be in the movie, fantastic!' But then he couldn't do it because he had to do something else, and it broke his heart. It turns out that Benedict Cumberbatch is busy for the next five and a half years. What is it with actors?"

Another actor they couldn't get was Idris Elba, although they do have the satisfaction of having launched his career in the TV series. One of his first acting roles was as a gigolo in a 1995 episode. 

"He doesn't like to say that," Lumley laughs. "It's never on his list of things he's done."

"He fled to America after," Saunders jokes. "But I'm so happy that we launched him. Because one of my favourite lines of Patsy's is when she sits on Idris' knee and goes, 'Can I talk to you like Sean Connery?' And he goes, 'No!'"

Watch the trailer for Absolutely Fabulous: