Welcome to Walmington

Mary Swinger still remembers the day when the Home Guard came knocking wanting to inspect the knickers of all female residents. Some devious fellow had been selling ladies' silk underwear made from a parachute and the men needed to determine whether it had belonged to the enemy. Naturally, the mission required the lifting of skirts.

Mary will have to get used to unannounced callers to her home enquiring about the underwear incident. For she lives in Nether Row, a line of ancient flint cottages in the town of Thetford, Norfolk. To the viewing nation it is better known as Percy Street, Walmington-on-Sea, the fictional setting for Dad's Army. From next month, fans will be able to follow a trail around the town taking in seven of the show's locations, including Nether Row, where scenes from four episodes were shot. A European Union grant will meet half of the £3,000 cost of producing the trail maps.

Dad's Army, which depicts the antics of a bungling but deeply earnest Home Guard platoon, ran from 1968 to 1977. The show, with its unforgettable song title "Who Do You Think You Are Kidding, Mr Hitler?" and sets that look as though they were made on Blue Peter, remains hugely popular today. Its videos, DVDs and overseas programme sales have earned BBC Worldwide almost £20m since the Eighties, making it one of the corporation's biggest classic comedies. It has been sold to Sri Lanka, Israel, Saudi Arabia, Belgium, Tanzania and, curiously, Germany. It is still regularly shown on television and is on the shortlist of programmes in the BBC2's current quest to find Britain's best sitcom. In 2000 a parade the society organised in Thetford, attended by several of the stars, is said to have attracted more people to the town than a visit by the Prince of Wales. Rather worryingly, according to Bill Pertwee, who played Chief Warden Hodges and is the president of the Dad's Army Appreciation Society, the series is now shown in US schools as part of their history education.

Thetford was chosen as a location because of its proximity to the MoD's Stanford Practical Training Area, which was ideal for filming a fighting force constantly practising for an encounter with the enemy (which they would lose even before reaching for their long-handled brooms). If one wonders at the characters' devotion to duty (members of the platoon were prepared to die rather than scarper when Captain Mainwaring, played by Arthur Lowe, and Sergeant Wilson, played by John Le Mesurier, found themselves cradling a bomb after it dropped on the bank), it is nothing compared to that shown by the man who found around 40 of the series 50-odd locations.

For the last six years Tony Pritchard, a local-authority supplies manager, has been driving the four-hour journey from his home in Gloucestershire to Thetford and the surrounding area five times a year in order to identify them. Tony, who stays for four-day stretches, likens his search to a fix of narcotics. "It's like a drug. It's a hunt, you get involved in tracking something down. The fact that it's a Dad's Army location is almost secondary," explains the bearded and bespectacled 52-year-old. "I started by trying to identify how many outside locations there were. Once I'd found a couple, I then thought, 'Where are the rest?' "

Armed with stills he had taken from videos of the series (he owns 26) Tony, who is the secretary of the Dad's Army Appreciation Society, would wander around showing them to locals in the hope of a glimmer of recognition. Some were surprisingly easy. "I was once taking a photo of a house and I wasn't sure whether it was right because I couldn't get the correct angle. A lady walked past, and when I explained what I was looking for she said: 'They filmed it from my garden. Do you want to see some photographs?' " Others were devilishly difficult - one railway station, for example, had been demolished. Tony dreads to think how much his preoccupation has cost him. On the bright side, he only has two more locations to find to complete his mission.

He initially produced a walking trail of some of the locations for fellow members of the society. When Thetford Town Council recently appointed its first tourism and marketing officer, he was asked to write one for the general public. "And this is the beginning of it," says Tony, suddenly getting animated. We are standing outside the Bell Hotel, where many of the actors stayed, across which still hangs a banner inviting customers to book for Christmas and the New Year. Inside, where Seventies classics are being piped unabashedly through the heavily carpeted corridors, is a plaque commemorating the gathering of the actors for the first day's filming.

A two-minute walk away is the Anchor Hotel, where other cast members were put up. In the restaurant the first scene of the first of 80 episodes was shot. This morning it is empty, apart from a smell of old-fashioned tearooms and rows of freshly twiddled paper serviettes at expectant place settings.

Up the Old Bury Road we come to one of the locations for "The Face on the Poster", which features a mix-up at the printers resulting in the face of Jones, played by Clive Dunn, appearing on a wanted poster instead of in a recruitment campaign. Here is the doorway through which a Polish officer walks, before spotting Jones and trying to arrest him.

A short distance away is the Newtown council estate. "I was looking for this for ages. I showed a photo to the owner of the B&B I was staying at and he immediately knew where it was," says Tony happily, standing in the middle of a quiet residential road. Here a scene from "Museum Piece" was filmed, in which a milkman brings back some guns Mainwaring has requisitioned from the museum on his horse and cart. Unfortunately, it is the same route as the milk round and the horse keeps stopping at every house, Tony explains. A scene from "The Lion Has Phones" was also filmed here, in which the platoon hides in large dustbins as part of their camouflage training.

Tony is very keen to get into the back garden of No 59, from where the crew shot the digging-for-victory scene in "The Showing Up of Lance-Corporal Jones". Wanting to take a photo of it, he walks up to the house, admitting that in such instances people often assume that he and his wife Julie, who often accompanies him, are Jehovah's Witnesses. "Let's see if the Dad's Army name works," he says, reaching for the bell. "In nearly every case as soon as you mention the words Dad's Army you're like a lost friend. But sometimes you get told to go away. The two questions people ask are: are you an anorak, and do you dress up? What they don't understand is that you are on the hunt trying to research something. It could be about any subject." Does he think he's an anorak? "I try not to be. I don't think I'm Private Pike or Captain Mainwaring or anything like that, I realise it's a fictitious storyline based on a real activity." Phew. There is no reply from the house, so Tony takes a photo from the back gate and says he'll come back later.

"A local historian thought it was this road, and then a resident confirmed it," Pritchard announces in Mill Lane, where part of "The Deadly Attachment" was filmed. The episode produced what was once voted by viewers one of the funniest lines in British comedy. Mainwaring's platoon is guarding a U-boat captain in the church hall and the German asks Pike his name. Mainwaring barks: "Don't tell him, Pike!" This is the street where the platoon is seen marching down to the harbour. Jones has a grenade down his trousers, the detonator of which is attached to piece of string that accidentally gets pulled.

Also on the trail is Thetford's bingo hall, a former cinema that appears in "A Soldier's Farewell" and "The Big Parade", and Walmington-on-Sea's town hall - Thetford's Guildhall - where "The Captain's Car" and "Time on My Hands" were filmed.

The latter, in which a German pilot dangles from his parachute caught on the clock tower, evokes particular memories for Thetford's town mayor, Derek Mortimer, now 71. Mortimer, then a member of the drama society, was one of many locals who became an extra, and played a fireman, tramp and ARP man. "I stood for hours looking up at what was supposedly the clock tower, but what was in fact a cherry picker. And in "The Captain's Car" I stood and stood. That was two days of filming in one place and I didn't come into shot," says the neatly bearded chap who wouldn't look amiss in a cravat and smoking jacket.

Mortimer's fond memories are of socialising with the cast in the Bell and Anchor. "I remember sitting in my car with John Le Mesurier drinking a bottle of gin throughout one afternoon. David Croft [the co-writer] had come up and said, 'For God's sake get him off the bloody set,' because he was fretting. John would fret, he would pace up and down. He had no patience. He said: 'Take him off to the pub where he will be happy' - and he was. And after the pub closed we sat and had a drink in my car. John Laurie [who played Private Frazer] was a different matter He was an extremely outgoing, friendly man. Bill Pertwee I got to know pretty well. Hodges was what you saw. Ian Lavender [Private Pike] was a bit vague. Arthur Lowe was exactly the same as he is on screen. He was short and an irascible sort of individual."

But Mary, whose house was used for a scene in "Man Hunt" in which a woman stands in the doorway being asked about her knickers, found Lowe perfectly charming when he asked to use her toilet. "They were fun. They weren't any trouble. My husband helped to put mud all over John Laurie's face [for "The Big Parade"]. And my daughter, Joanne, who was about seven or eight at the time, fell in love with Ian Lavender. He came to say goodbye to her. I've got photos of my son with Clive Dunn and James Beck," says the 63-year-old, rushing upstairs to dig them out.

Mary and her husband are now the only residents of Nether Row who were there during the filming. Once enthusiasts start pitching up in droves, Mary's enthusiasm for sharing her memories may wane. Today, handwritten signs on her door and windows warn: "No parking". Perhaps they will soon be replaced by others that read: "No callers for knickers anecdotes".