This Odeon Blu-Ray costs £15 at the moment. It will doubtless come down in price.

Michael Reeves was the doomed wonder kid of 60s British horror. He only made three films, but his reputation is unshakeable. It largely rests on this film, released in 1968, the year horror got modern (1968 also saw Night of the Living Dead and Rosemary's Baby). Produced by Tigon, the most interesting of the British exploitation production companies, it's a period gothic that eschews the cosy certainties and wobbly production values of Hammer. It is instead a cynical but beautiful film about how evil men will exploit the prejudices of others to their own profit. It is essential viewing.

During the Civil War, Matthew Hopkins and his thuggish assistant John Stearne ply their trade as witchfinders, sentencing the innocent to torture and execution for financial gain and sexual pleasure. A young Roundhead soldier, Richard Marshall, having seen his fiancée's family victimised, makes it his mission to bring Hopkins' career to a premature end.

Everything about this film suggests it should be an old-fashioned horror of the kind that were churned out in great numbers in Britain in the 60s. The costumes, the time period, the locations (lots of taverns and isolated villages); and most of all, the star. Vincent Price is beloved of horror fans, but you generally knew what you were getting with him: high camp posturing; noble suffering with a raised eyebrow and a wink at the audience; and over reliance on his honeyed voice. Reeves, the director, had wanted to cast Donald Pleasence (just as mannered in his way, but less obviously hammy). Price was forced on the film by AIP, the US studio that put up some of the money. Miraculously, Reeves manages to get a 'proper' performance out of Price, restraining him from the eye-rolling and hand gestures that he normally used. Despite what some fans say, this isn't Price's best performance - he was *good* at high camp, and his performances in the Edgar Allan Poe films are excellent - but it's fascinating to watch him having to be genuinely sinister. You can almost sense his frustration at not being allowed to coast through the film on autopilot, collect his fee, and fly home.

The rest of the cast are very good. Robert Russell is excellent as Stearne, Hopkins' uncomplicated, sadistic henchman. A young Ian Ogilvy is romantic and frightening as Richard. Hilary Dwyer is totally lovely as Sarah, his victimised fiancée. The film even sneaks in a weird cameo by Wilfrid Brambell.

Apart from Brambell's scene, this is a humourless film. It's almost The Crucible done as horror. Needless to say, there are no witches. There are simply people denounced by their malicious neighbours, and it perfectly captures the meanness of spirit that makes people want to destroy those who don't conform to their worldview. Hopkins and Stearne are exploiting nastiness that's already there, mouthing pieties as they pocket the rewards for executing witches, and getting their jollies with the local wenches before they do (it must be said, Price doesn't look too comfortable during his one seduction scene). There's no release from this world at the end of the film, even if this story reaches its conclusion. The pointlessness of revenge is driven home, as is the impossibility of fighting against a society proud of its own ignorance.

It was controversial in its day, and still has an 18 certificate. But the violence isn't exaggerated (except at the film's climax), and is deployed sparingly. It's based on a true story (although one of the execution methods looks unlikely) and follows one of Hopkins' more notorious cases. It's best seen as a period drama with outbreaks of horrific violence, rather than a straight horror movie. It's also unusually beautiful. All shot on location in Suffolk, the beautiful English countryside and sky naturally reminds you of Constable. Shots are often framed to emphasise the beauty of the foliage as men furiously gallop past in the background.

It's often (perhaps too often) been called an 'English Western', and the basic revenge plot and frequent emphasis on horse-riding back that up. But it's also one of the great English pastoral movies (the lovely music, which evokes Greensleeves, adds to this feeling). Perhaps the heavy emphasis on nature is intended to contrast with the artificial religious structures put in place to control people. As a radical late-60s filmmaker, Reeves probably took a dim view of traditional religion, although Hopkins is only pretending to be a Christian.

But any messages the film has (and it has plenty) don't get in the way of the story; they enhance it. Reeves died shortly after making this film, which is a cause for regret. But at least he left us a couple of great horror movies, and this is the greatest of them.

I was dubious about this getting a Blu-Ray release, as it seemed too old and too cheaply made to be worth enhancing to HD. Happily, my doubts were misplaced. It looks stunning. There's a certain amount of grain in the image, but that's to be expected for a film of its vintage. Just in the first few minutes I was delighted with the amount of detail visible in the plants in an early forest scene - the ferns looked especially good. Costumes, sets, hair all look so much better than on DVD. Once again, Blu-Ray has taken one of my favourite films and made it better. It does make it easier to spot telephone wires in the background of one shot, though, as well as some woeful cloud-related continuity errors.

There are plenty of extras, most not in HD. We get the US versions of the opening and closing credits (the film was called Conqueror Worm in the States to try to make it seem like another of Price's Poe movies). There's also a raunchier version of one scene for the European market - it's just a tavern scene with some naked boobs in it. There's a rather irritating, talky trailer and a bland image gallery. A short, completely silent black and white amateur film made by Reeves as a youngster is unimpressive.

There's a 25-minute documentary about Reeves, which was made for Channel 4's excellent Eurotika series in 1999. It features various friends and collaborators, and wheels out some now-legendary anecdotes. All good stuff, although it's on at least two other DVDs I own. There's a ten-minute clip of Vincent Price on ITV talkshow Aspel and Company. Price is a great raconteur and a deeply endearing guy, but Witchfinder General isn't even mentioned, and the tone is very lighthearted, rather at odds with the film and other extras. And there's a history programme about witch hunts, part of a series called 'Bloody Crimes', much of which is devoted to Hopkins. It's interesting, I guess, although marred by poor acting in the reconstructions and absurdly hammy camera-work.

The most baffling extra is the commentary. A guy who wrote a book on Reeves is joined by Michael Armstrong, a late 60s horror director who made a couple of terrible films, and apparently knew Reeves. Bits of it are mildly interesting, but Armstrong frequently starts talking instead about Mark of the Devil, a sleazy European witchfinder film he made in 1970. He still seems convinced that the two films are roughly equal in quality. They are not. Witchfinder is a masterpiece, while Mark of the Devil is no different to other cheap, sleazy witchfinder movies churned out at the time to cash in on Reeves' film (The Bloody Judge, for instance, or Cry of the Banshee). A weirdly pointless endeavour.

Still, I'm delighted to see a film like this get the Blu-Ray treatment. I hope we get some other classic Brit horrors - Blood on Satan's Claw and The Wicker Man being the obvious choices.