On the face of it, Thetford, the former "Capital of East Anglia", wasn't the most obvious place to film Dad's Army. The series came to life in the imaginary south coast town of Walmington-on-Sea, the closest point across the Channel to the German Menace. Real-life Thetford, however, is a good 30 miles from the coast.

But that's a minor difficulty in television terms. It had the right 1940s period feel (well, parts of it did) and a military training area just up the road could come in very handy. But – permission to speak, sir – what about seaside sequences? Simple: film them in Lowestoft or Great Yarmouth. So they did, from 1968 to 1977. Thetford, in south Norfolk, launched its own Dad's Army Trail four years ago. Together with guided tours, it has – to everyone's astonishment – pulled in some 5,000 tourists.

"I thought that 30 years on from the final episode, there wouldn't be much take-up, but the interest in the series is phenomenal," says Stuart Wright, who leads many of the tours. "People come from Australia, Canada, wherever it has been shown. I thought it would just be older people, but we get coach parties of youngsters who've seen it on UK Gold. There's a real warmth towards it."

A Dad's Army museum, full of memorabilia of Walmington Home Guard's cherishable incompetence, opened late last year, and a statue of Captain Mainwaring, the platoon's preeningly pompous leader, is planned: sitting on a park bench, impatiently waiting for tourists to sit next to him.

And, on the 26 and 27th this month, the town will stage a Dad's Army weekend, with guest appearances by Corporal Jones's butcher's van, the Norfolk Home Guard Re-enactment Society, and "Jill Daniels and her Hits of the Blitz show".

It's all quite surreal. Perhaps the reference on one Thetford website to "Dada Army" isn't just a simple misprint, but a tribute to the series' cosy British brand of Dada, the bizarre early 20th century artistic movement that valued anarchy and chaos. But don't panic, Mr Mainwaring. Stuart Wright, a chartered accountant, town councillor and chairman of the civic-minded Thetford Society, takes me on a walking tour. Wright is steeped in the series. He has watched all the surviving 78 episodes, noting just one passing reference to Thetford. "In the first episode, someone says, 'Mrs Hoskins is on the phone to her sister in Thetford'."

As we troop round, he points out a doorway used in one episode, a council house window used in another and the street where the platoon camouflaged themselves with dustbins. He pulls film stills from his shoulder bag to compare nostalgic fiction with present-day reality. Finally, we reach the town's Guildhall, where, in a celebrated episode, a German parachutist dangled from the clock tower.

"I remember coming to watch the filming as a nine-year-old," says Wright. "And I didn't think that 35 years on, there'd be any interest in these…" He delves in the shoulder bag and brings out the snaps he took with his Brownie camera. At first glance, all this seems
par for the course in Thetford, apparently a pleasant backwater of suburban England, full of Walmingtonian charm: a bungalow called "Dunweedin" (its front garden has been concreted over), a sponsored hanging basket scheme (a town-centre board lists all 62 sponsors), a Conservative Club with a framed picture of Churchill, a Royal British Legion with pictures of the Queen and Prince Philip gazing down. Near the vast Castle Hill, England's tallest medieval earthwork, the Thetford Time Line seems to spell it out: "1066: Thetford ranked sixth in size of English towns… 1156: Thetford dropped from the list of important English towns."

Centuries were to pass, many uneventfully, until Thetford became a London-overspill town in the late 1950s and its population tripled in 10 years. Part of the historic centre was cleared to create a "modern" precinct that now looks grimly dated. "People say that, if it had been left as it was, Thetford would be a World Heritage Site now," says Wright, pointing out that an urban regeneration scheme is underway, to repair some of the damage. In more recent years, there's been an influx of Portuguese migrants, who now make up an astonishing 8,000 of the 28,000 population and have won the town the nickname "Little Lisbon".

There's plenty to see, including many houses attractively faced with flint, which resembles black and grey fish scales. "They used to say that in the rain, Thetford shone," says Wright, as we reach a statue of Thetford-born Thomas Paine, the 18th century political radical and author of The Rights of Man.

"Recently voted 33rd Most Famous Briton," Wright points out. "One place lower than David Beckham." The gilded statue, showing Paine apparently hailing a taxi, dominates the main street. It begs to be given a Dad's Army theme: The Rights of Mainwaring?

Round the corner, the engaging Ancient House museum, with its 15th century wattle-and-daub walls, celebrates Duleep Singh, a Sikh maharajah who settled nearby and married his chambermaid.

Thetford is the gateway to the flat and ancient landscape of Breckland, an appealingly wild and lonely area of rough heathland, forest and twisted pines, one of England's least-populated areas.

A day's drive takes me to East Harling church, where a warden offers binoculars for a better view of the great 15th century east window. From there, a walk along the intriguing Great Eastern Pingo Trail (pingos: primeval ice-mounds that collapsed and formed crater-like ponds). Damselflies hover, a tiny muntjak deer darts into the undergrowth, the only sound is birdsong. Lunch in Swaffham, once one of Norfolk's most fashionable market towns, still handsome in an unpretentious way, and, only an hour or so later, tea in Castle Acre,
a delightful French-feeling village almost overstocked with great buildings: castle, priory, and St James's Church.

On the way back to Thetford, a double rainbow suddenly arches over fields of poppies, the sky darkens ominously and rain buckets down. But the strategy is clear: "Don't panic!"

The friendly, central and comfortable Wereham House Hotel (01842 761956; www.werehamhouse. co.uk) has doubles from £74 per room per night, B&B. Thetford tourist information: 01842 751975 (www.explorethetford.co.uk).