The publicity blurb that accompanied The Wicker Man's release into British cinemas 25 years ago said it best: "They do things differently on Summerisle." They lure upstanding police sergeants off the distant mainland with rumours of a teenage girl who has mysteriously vanished. They provoke the "Christian copper" with midnight orgies on the village green and confound him with contradictory accounts of the girl's fate. And then they declare that everything has been a fiction.

The hunter is really the hunted. The crops have failed and the newly revealed pagans of Summerisle require a blood sacrifice. On a hilltop stands he terrifying wicker man, a 60ft human effigy used, say the legends, by Celtic druids to imprison and burn those they offered to the gods. As the flames rise and Sergeant Neil Howie of the West Highland constabulary screams his own last rites, the natives of Summerisle far below him dance and sing, secure in the conviction that the old gods have been appeased.

Huh, you're saying, just an average Saturday in Stornoway. There is little, however, about The Wicker Man that is average, easy, precedented or predictable. If British cinema is a production plant of the mediocre, churning out modest slices of whimsy and social realism, then The Wicker Man is a misshape, shop-soiled, fire-damaged goods. Like a strange deadpan amalgam of Brigadoon and Rosemary's Baby, The Wicker Man blends ripe eroticism with theological debate, folksy frolics with Presbyterian frigidity, to produce a film that forensically examines Scotland's religious and cultural bipolarity, it's vacillation between the celebratory Celtic traditions and the empirical iciness of Calvinism.

In America, where The Wicker Man has always found a fanatical audience, it is known as "the Citizen Kane of horror movies" but at home it remains the freak that British cinema tried - and failed - to keep locked in the West Wing.

Made on a shoestring budget, threatened with closure during production, then slashed to ribbons on its release, The Wicker Man suffered enough to allow its makers some insight into its hero felt on that hillside. Edward Woodward, who played Howie, remembers that " when we were filming The Wicker Man, we all thought it would be the making of our careers". But it was not to be: the film was denied a proper release, eventually limping into cinemas only as a support feature to the inferior Don't Look Now.

Subsequently, 20 crucial minutes of footage disappeared in some anonymous cutting room. When the movie went to Cannes, a full-size wicker man was erected on the Croisette - but the print of the film went missing. Back in Britain, Christopher Lee, who played the charmingly sinister Lord Summerisle, and director Robin Hardy tried to cultivate an audience by offering to buy tickets for film critics. It was too little, too late. The Wicker Man was quietly buried and sold to a tax shelter company I America, the directors of which were later jailed for obtaining films fraudulently. In 1977, the National Enquirer reported that Rod Stewart hoped to buy the film's negative and burn it to avoid the public seeing his then girlfriend Britt Ekland as Willow the barmaid, nakedly tempting the uptight, virginal Howie. Stewart planned to burn The Wicker Man forever. He denied the rumour n a recent interview. "But yes," laughs Hardy today, there does seem to be some kind of curse around The Wicker Man. That's what happens when you meddle with the dark forces, I suppose."

If there ever was a curse around The Wicker Man it has obviously lifted n recent years, for the film has undergone an extensive rehabilitation. Two years ago, a reader's poll in Empire film magazine named it the greatest British film of all time and it has enjoyed a nationwide cinema re-release as part of the Primal Screen season. The Wicker Man soundtrack has become a huge seller since its release this year, while this month brings issue one of Nuada, a quarterly Wicker Man magazine, and the broadcast of BBC Scotland's Ex-S documentary on the worldwide cult that surrounds the film, maintained through websites. Later this month, the Glasgow Film Theatre hosts a Wicker Man night, a taster for the Wicker Man convention to be held in January in Dumfries and Galloway where much of the film was shot. Canal Plus, the French company that now owns The Wicker Man, has just licensed the rights for a Hollywood remake with Liam Neeson reprising the role of the duty-bound God-fearing sergeant.

Now, even Lord Summerisle himself concedes something strange is going on. The Guinness Book of Records lists Christopher Lee as appearing n more films than any living actor and he can easily name his favourite among them. Over lunch, Lee remains the ceiling-scraping embodiment of heavy presence, speaking in a voice that seems to start somewhere around his ankles, choosing his words as if they were his next victim.

Lee still carries a torch for the film, promoting it at every opportunity, pointing out that his faith in Anthony Shaffer's script was so great he deferred his fee in lieu of a slice of the profits - which never came, of course. He is particularly keen to dispel notions that The Wicker Man was another of the schlocky gothic chillers that made his name.

"People call The Wicker Man a horror movie," he says, but it isn't really, it's far more subtle and sophisticated than that. Horror is about decay; The Wicker Man is about an opposition of values, the struggle to achieve spiritual growth. Without doubt, it is the finest film I've ever been involved in.

"It's a flawed masterpiece," he continues. "The film we shot was a masterpiece but then it was messed about with, butchered almost. It's my dearest wish to find the missing footage and reassemble The Wicker Man as it should be. But I far it's lost forever, probably hidden in a mislabeled can, buried in an archive somewhere."

Edward Woodward last set foot in the Ellangowan hotel, Creeton, 25 years ago. Back then, it doubled as The Green Man, the Summerisle pub where licensing restrictions didn't apply and the regulars hollered lusty choruses of The Landlord's Daughter into the small hours.

In reality, the Ellangowan remains a quiet country pub where local trade is supplemented by a flow of Wicker Man fans from as far away as America. It is still recognisably Summerisle's den of iniquity as Woodward, here on a tour of Wicker Man locations, can't help but notice: "My God," he jokes, "the locals are still sitting in the same places."

This is the heart of what fans call "Wicker county", a mosaic of locations in southern Dumfries and Galloway. Film trickery gimmicked the fictional Summerisle out of closes in Kirkcudbright, graveyards in Anworth, hotels in Newton Stewart and Gatehouse of Fleet and a bleak clifftop campsite on Burrow Head, Isle of Whithorn, where the wicker man was erected. Today the only remnant of the 60 ft structure is a two inch sprig poking out of the grass, yet it is a site of pilgrimage if the bottletops and cigarette ends strewn around are any indication. Cemented into a nearby cove, sheltered from the Atlantic winds, remain a set of Wicker man legs, left over from a trial burning.

In the Ellangowan, a showing of the film has been arranged in Woodward's honour. A fiddler plays tunes from the films; locals compare souvenirs from the time when the 80-strong production crew monopolised their world for seven weeks. Woodward casts a glance around. "This is a very strange feeling,' he reflects. "It's like I stepped out for 10 minutes, 25 years have passed and I came back in again.

Two strapping lads in the corner appeared a s schoolboy extras; Ian and Sandy Foster declined a wedding invitation to watch the orgy scene being filmed, but it was rained off; Deirdre Murray was the on-set nurse who repaired Woodward's broken toe; Jane Jackson appeared as Ekland's "bum double" when the actress refused to allow here naked behind to appear in a seduction sequence.

In the places where The Wicker Man set its foot, feelings toward the film are mixed. The older set regard it much as Howie did the islanders: as a slightly seedy, somewhat unnecessary entity that gives decent folk a bad name. Those in middle age look back in embarrassment at the film's 1970s fashions, at the reminders of old flames and ill-advised hairstyles. "When I stood in for Britt Ekland," says Jackson, "I had to make sure my parents didn't find out. Now I like to keep it quiet in case my daughter gets ribbed at a school." Galloway folk, though, are an unusually friendly lot; the trekkers, the pilgrims, the calls to tourist information in Dumfries are received warmly, albeit with a seam of bemusement at how this strange phenomenon fell into their lives.

Memories here are long and nobody mentions The Wicker Man without recalling the Ekland Incident, when the actress arrived on location and promptly described Newton Stewart 'the worst place in creation", a haven of alcoholism and illegitimacy. "Gloom and misery oozed out of the furniture," she added.

The full panoply of civic derision was unleashed and the skirmish made the national papers. Newton Stewart provost Archie Plunkett hit back first: "I saw Miss Ekland at various functions; she seemed quite capable of downing great quantities of drink." One Mr McNeil told the Galloway Gazette that "the best thing for her would be to have her bottom spanked."

Eventually Peter Snell of British Lion, the film's producer, issued an apology on Ekland's behalf. "Mind you," says Frank Ryan, a local journalist, "I saw her unveil a statue at Gretna Green last year and she was fine, so maybe she has matured."

Today, the British Lion logo has been proudly reinstated on the door of Snell's office at the Pinewood studio complex. A fixture of the British cinema scene since 1917, British Lion was churning out film versions of television sit-coms when writer Anthony Shaffer, Christopher Lee and director Robin Hardy approached Snell with the idea for a quirky, low-budget thriller, set in Scotland. Snell was hooked; The Wicker Man went before the cameras in October, 1972.

As production neared its end, however, Snell was sacked and replaced by two managing directors who declared they wanted no part of The Wicker Man. "Fairly common politics in the film industry," says Lee. "The new men come and make themselves look big by rubbishing the work of their predecessor." When Lee, however, smuggled a print into France and the film took the Grand Prix du Film Fantastique at the Paris Film Festival, British Lion capitulated, releasing the film as a B-feature, albeit savagely edited.

And there it foundered, passed from one uninterested holding company to another, until Hardy attempted to assemble a definitive print in the late 1970s. Sections of the film had disappeared entirely, but a near-complete version was achieved and released into American art-house cinemas. The results were instantaneous. "I was actually passing a theatre in San Francisco," says Snell. "There were queues round the block, people standing three deep. I asked someone, 'What's on?' 'The Wicker Man,' the guy said. 'Ever heard of it?'"

Now, 25 years on, what accounts for The Wicker Man's deathless popularity? "The writing," says Woodward. "It was all on the page. Shaffer simply wrote a wonderful script."

Lee concurs: "It was a very serious production, about gravely serious issues" - a remark that hints at why history has vindicated the film. To its 1970s audience, The Wicker Man probably felt like a singles' night in a folk club but the contemporary viewer is better placed to appreciate its strangely clairvoyant quality.

Clairvoyant in the sense that issues at the film's heart have become more pressing in the years since production, particularly Christianity's battering by the rise of non-orthodox neo-faiths. Yet at the film's heart is the contention that all religions are mere social constructs, devoid of any true moral authority. Howie dies pointlessly, the islanders pray for a harvest that may never come - all is a matter of blind, never resolved faith. When you remember that Britain's church leaders managed to orchestrate a nationwide ban of Life of Brian for its mild heresies in 1978, you realise how unpalatable The Wicker Man's message must have been.

Conflicts between science ad religion, between men and women, between the civilising power of the urban and the brutality of nature also animate the film, augmenting the fast sex and creepy blankness that guarantees any movie cult status. The Wicker Man, however, remains the cult of cults, a film truly ahead of its time, and one whose memory will burn for years yet.

Taking his leave form the Ellangowan hotel, Woodward struggles to accept his strange fate: 'It's weird, you do a film, it's just a job, you forget about it, and that's usually that. But there's something about The Wicker Man that's different. It keeps coming back, keeps lodging in your brain. There has never been anything like it and there won't be again."