How Dad's Army came to the screen
Fans of Dad's Army have plenty to look forward to over the next few weeks.
The long-awaited Dad's Army movie - staring Toby Jones as Captain Mainwaring and Bill Nighy as Sergeant Wilson - is set to hit cinema screens in February 2016.
But before that comes a one-off BBC Two drama We're Doomed! The Dad's Army Story which shows how writers Jimmy Perry (Paul Ritter) and David Croft (Richard Dormer) overcame BBC management scepticism to bring the hit sitcom to the screen.
"I won't lie," admits Charlotte Surtees, the TV drama's executive producer. "We were keeping an eye on what they were doing. We felt that our project was complementary and not at odds with what the feature film was attempting to create.
"I think they have a tough job. They have a fabulous cast but we have an equally fabulous cast."
Among the other famous names in We're Doomed! are Julian Sands as John Le Mesurier (Sgt Wilson), Mark Heap as Clive Dunn (Corporal Jones), Shane Richie as Bill Pertwee (ARP Warden Hodges), and Kevin Bishop as James Beck (Private Walker, the cockney spiv).
Surtees says there were no casting clashes between the TV drama and the movie. "It didn't pose a problem because we were casting in a very different manner to the film. We needed our Arthur to be Arthur Lowe first and foremost and Mainwaring second."
Sessions, who has an uncanny likeness to Lowe in the TV drama, reveals that Toby Jones had sent him a note saying: "Best of luck with your Arthur."
He admits he felt "great pressure" playing such a national treasure.
"He's been been a huge hero of mine ever since I was 14 or 15," Sessions says. "He had an incredible capacity to make you laugh or smile when he was saying something pretty anodyne and non-committal.
"Arthur's got a very beautiful voice. It's quite sonorous. Even though he would fluff lines constantly it didn't somehow matter. He was just so wonderfully Captain Mainwaring."
On TV between 1968 and 1977, Dad's Army attracted 18 million viewers at its height. We're Doomed! has the blessing of 92-year old Jimmy Perry. Co-writer David Croft died in September 2011.
The drama shows how Perry's inspiration came after seeing a group of soldiers jogging in a park in May 1967. Within months he had written the first script of The Fighting Tigers - the original title of Dad's Army.
Other fascinating details emerge, such as Ian Lavender bringing his own scarf on set to wear as Private Pike and Clive Dunn finding the line "they don't like it up em!" too rude.
"There's very little in the film that's made up," notes Surtees. "It's essentially the story of two men going through a midlife crisis."
Both Paul Ritter and Richard Dormer watched old interviews with Perry and Croft to help them get into character.
"We were both slightly taken aback at how terribly posh and BBC-ish they both were," says Ritter.
"They were two personalities waiting to meet," adds Dormer. "And when they did they clicked, and had the same goal - which was to save their careers."
Why do they think Dad's Army has been such an enduring hit?
"Croft and Perry had brilliant ideas," Ritter says. "They created characters that leapt out at you, but they also knew what to do with them. The inversion of Wilson and Mainwaring's social status and professional status was brilliant."
"The characters endure because they are loveable," adds Dormer. "I think there's a soft fuzzy warmness about Dad's Army that people remember.
"I met David Croft. He was a man of few words. But he had great charisma."
We're Doomed! The Dad's Army Story will be on BBC Two on Tuesday 22 December at 21:00 and repeated on Christmas Day at 22:20.