Steve Pratt talks to Helen Mirren, Celia Imrie and director Nigel Cole about the challenges of bringing to life the true story of Yorkshire WI members who cheekily stripped off for charity and ended up in Hollywood.

Sensitive shooting was required to ensure the film gained a Christmas week release in the US.

Appearing in Calendar Girls taught actress Helen Mirren just how extraordinary so-called ordinary people can be. The story of the women in a Yorkshire WI who bared all for a charity calendar, sparked off a craze to strip off in a similar manner, and ended up in Hollywood, is the stuff of movies. The fact that it's true makes it all the more out-of-the-usual.

"Filming in Yorkshire I learnt that behind every door, down every street there's a potentially extraordinary person," says Mirren.

"We swan around our acting world and everything is horribly celebrity-driven, but I realise how extraordinary ordinary people are.

"There's the smallness of the communities these characters come out of and the strength of these communities. We were so welcomed by them. I'm sure we must have pissed off a lot of people with our trucks and the rest of it, but I never felt it."

Mirren joins a host of familiar British actresses - including Julie Walters, Celia Imrie, Penelope Wilton, Annette Crosbie and Linda Bassett - in the fictionalised story of the calendar girls of Rylstone WI. What everyone wants to know about, of course, is filming the scene in which they strip off to pose for the calendar.

She assumed the role of leader, partly because her character is the moving force behind the calendar and also as the actress is a veteran of getting her kit off for the cameras. She'd come top of the list of actresses who strip on film in a survey in a TV programme shown only days before - a fact, Mirren says of which an ex-boyfriend had called to inform her.

She accepts the dubious honour in good part, laughing about both it and a quote in which she declared she wasn't doing any more nude scenes.

"I was probably quoted before I did this film," she says. "Of course, you say that and in the next movie you're asked to do it and it's an essential part of the role."

The film marked Celia Imrie's first nude scene and, to make matters worse, she was the first to be filmed dropping her robe. "I think it's one of my biggest dares," she says. "I don't even like taking my clothes off in front of myself. But I was rather thrilled I was going to be the first, although I don't think I'll do it again in a hurry.

"There was a marvellous lack of vanity about us all. Helen was marvellous, holding my dressing gown the minute I had to take it off and there for me the minute I had to put it back on. We were not actressy or luvvie, we just got on with it and helped each other like pals."

Director Nigel Cole points out that in many ways, the actresses stripping was a replay of what the real women went through photographing the calendar. Imrie says: "We knew we had to get on with it as they did. They were braver and did it in real life, and had to face the onslaught afterwards."

Cole main concern wasn't filming the scene, but how much he could show on screen to get a PG13 rating in the US, where the film opens on Christmas Day. "I did have some amusing conversations with our lawyers at Disney in Hollywood about how many nipples could be shown," he says.

"It's a very discreet film, so I don't think there will be any problems. What history has shown is that cinema audiences around the world love films about what they see as conservative English characters being naughty. There's already a huge buzz about this film in Japan. I don't know what they'll make of it."

The film, like the real story, doesn't stop with the publication of the calendar. It follows the women as they travel to Hollywood where they appear on the front page of newspapers and TV chat shows.

"When you ask the women they talk for 15 minutes about making the calendar and eight hours about what happened after that. So much came out of so little," he explains.

"This extraordinary adventure was the really hard thing to get right, and the scary thing is that the climax, making the calendar, comes in the first third of the film.

"The interesting part is afterwards. The idea of ordinary housewives being treated like movie stars in Hollywood seemed to be fresh and original."

Mirren says she doesn't know if it's "a Yorkshire thing" but this group of women had the ability to enjoy and love whatever is thrown at them.

"They go off in a most fantastically innocent and free kind of way. They just enjoy it and express how much they enjoy it," she says.

"I didn't want to do an impersonation of Tricia Stewart, whom my character is based on. I didn't study her for gestures or anything like that. The over-riding thing when we met the women was you couldn't go too far in acknowledging their enjoyment of what's happening and commitment to anything they're involved with."

The actresses had as good as time as their real life counterparts. Mirren points out that actresses rarely get the chance to work with a lot of other actresses. Most of their professional life is spent with groups of men or boys, whether in plays or films.

"It was an incredible pleasure, and helped by the fact that we aren't young and competitive in that way. Sometimes it's easier to be older. Professionally, we are all on an even keel. We could just encourage each other, enjoy each other's company and inspire each other."

Calendar Girls (12A) goes on general release Friday September 12