As Dad's Army marches onto the big screen, Susan Griffin rallies the troops to sniff out some behind-the-scenes gossip on why they signed up for duty

1 We have The X Factor to thank for inspiring the idea of making a movie. Producer Damian Jones, 51, was flicking through the channels one night, in a bid to find something aside from the TV singing show to watch, when he came across a rerun of Dad's Army. Curious, he tracked down the viewing figures and discovered that almost three million Brits were still tuning in every week to watch the nostalgic comedy series about a Home Guard platoon, which first aired in 1968. Inspired, he then approached the Dad's Army estate with the idea of making a movie.

2 Screenwriter Hamish McColl was understandably nervous about embarking on the script. "Of course, this was the holy grail of British comedy in many ways and there are a lot of arguments to leave it alone," says the 54-year-old, whose other credits include Mr Bean's Holiday. "But there is such richness and depth in that wonderful idea that Jimmy Perry and David Croft had, and such wonderful characters, that there really was mileage in it."

3 For McColl, the real-life subterfuge campaign that had been thought up, to throw the Germans off the scent of their real Day-D targets, offered the perfect comic potential. "I saw photos of members of the Home Guard holding up inflatable tanks and balsa wood planes, and I thought, 'This is Dad's Army!" he says. "It's got all the aspirations of war, and all the comedy of inflatable tanks."

4 Director Oliver Parker, along with Jones, was looking for actors who could make the iconic characters their own. "We were very clear that we were casting Captain Mainwaring, not someone doing Arthur Lowe doing Captain Mainwaring," notes the producer. Toby Jones, 49, was top of the list from the offset. "The fact I've cast a smaller guy is not to do with Lowe, but because this idea of Mainwaring as a little Napoleon leading the platoon seemed intrinsic to me," Parker comments.

5 The film-makers found a certain momentum. "It became something we could all do together, and all sink together if it failed. There's something very Dad's Army about that," says Parker, laughing. Danny Mays signed on as spiv Private Walker, Blake Harrison as the dreamer Private Pike, Bill Nighy as the smooth Sergeant Wilson, Sir Tom Courtenay as the bumbling Lance-Corporal Jones, and Bill Paterson as the doom-laden Private Frazer.

6 Unlike the TV series, women have prominent roles in the film, with actresses including Sarah Lancashire, Felicity Montagu and Annette Crosbie all taking part. "The cherry on the cake", as McColl puts it, "was Catherine Zeta-Jones joining us to offer that wonderful lustre of glamour." Parker adds: "She really connected with the script and when this calibre of cast was joining up, she didn't seem to hesitate."

7 The Welsh actress plays the mysterious femme fatale, Rose. "The men are competing for her attention, which is always fun," says the 46-year-old. "She's flirtatious and plays around with these guys, which happened off set as well." She freely admits there are times when she's used a little flirtation to get what she needs. "Some women would go, 'Urgh no', but I have been a bit flirtatious to gain in my past," she confesses with a laugh.

8 On-set flirtation is news to Harrison. "I think it was the older boys," says the 30-year-old actor, grinning. "I reckon it's Tom. Tom's a ladies' man, a charmer." Best known for plating the gormless Neil in The Inbetweeners, Harrison admits he had initial reservations. "There is that thing where you don't want to keep playing dumb Cockneys, but ultimately, as soon as I'd read the script and chatted to Olly [Parker] and he started mentioning the cast, you're like, 'Yeah, I'd probably be a bit silly not to get involved with this'."

9 For Parker, one of his favourite moments was Jones trying to submerge himself in water off the East Yorkshire coast, where the film was shot, while wearing a fat suit. "But he couldn't, he was too buoyant," he recalls, laughing. There was also the moment when, as Jones puts it, "I was upstaged by a seal". "I couldn't work out what I was doing. I thought, 'God, I'm a comic genius! Look at that - I just need to come out of the water and I get this big laugh'."

10 Off camera, Harry Potter star Michael Gambon, 75, is credited with keeping the troops entertained, by sharing his showbiz anecdotes. "It's unusual for Michael to do that," jibes co-star Paterson, 70. "I've only worked four or five times with him over the years and it has never happened before: I'd never heard any of these stories." Gambon insists that Paterson is "just as bad as I am". The pair would eat out together most nights during the shoot, which unsurprisingly caused a few double takes. "Yeah, there were people being nosy, looking through the windows," notes Gambon. As Paterson puts it: "Having dinner with Dumbledore every evening has its ups and downs."

  • Dad's Army is in cinemas now