Treat Psychomania as a straight-faced attempt at addition to the witchcraft-in-suburbia genre and it’s doomed to failure, its mostly awful acting, terrible dialogue and pedestrian directing sinking it without trace. Treat it as a comedy though and it’s a riot, managing to overcome the sheer lunacy of its plot to entertain almost in spite of itself. It’s certainly one of the oddest British horror films of the 1970s, quite some feart when you consider what it was up against.

There’s a dash of what would later become “folk horror” about the proceedings, with its emphasis on witchcraft, standing stones and some never explained business about demonic frogs, but all of that is soon beaten into submission in the roar of an engine and the weirdness of Arnaud d’Usseau and Julian Zimet’s screenplay (next up for them was the similarly odd Horror Express (1972)).

It begins with a nicely atmospheric title sequence of motorcycles riding in slow-motion around a fog-shrouded stone circle, but director Don Sharp either can’t or wasn’t particularly interested in maintaining the eeriness and it’s about as creepy as the film gets. The riders are members of The Living Dead, one of cinema’s least intimidating biker gangs. Led by Tom Latham (Nicky Henson), they count among their ranks Tom’s girlfriend Abby (Mary Larkin), who seems to be far too nice to be mixed up with these reprobates, Jane (Ann Michelle), Hatchet (Denis Gilmore), the musically inclined Chopped Meat (Miles Greenwood), Gash (Peter Whitting), Hinky Rocky Taylor and Bertram (Roy Holder) – yes, they’re that terrifying these Home Counties Angels that they have among them a biker named Bertram…

When leading his gang on petty and childish missions to terrify shoppers in Walton-on-Thames (cue “comedy” business involving a man on a step ladder and anther carrying a tray of baked goods), Tom lives with his mother (Beryl Reid) and her butler Shadwell (George Sanders) in a suburban home that screams 1971 at deafening volumes. Reid wafts around in diaphanous gowns, her home littered with “space age” portable television and objet d’art, the walls covered in starry wallpaper and odd geometric shapes that were probably meant to suggest a rarefied affinity with the current modern art scene. Mrs Latham, it transpires, is a witch who made a pact with the Devil, trading Tom’s soul for immortality and when Tom finds out on his 18th birthday, he presses his mother for more details. There’s something here about their frog god but it’s not at al clear whet it’s meant to be or why they’re worshipping it, put the upshot is that Tom learns that he can also attain immortality by killing himself and simply believing that he’ll return from the dead. If only we all knew it was so easy…

After death, Tom is buried by his gang, fully clothed in his leathers, bolt upright on his beloved bike, and Chopped Meat takes up his acoustic guitar to regale one and all with a celebratory ditty titled Riding Free (“He really got it on/he rode that sweet machine just like a bomb”). To Greenwood’s credit, he does actually seem to actually be playing the right chords on his guitar and no matter what Mrs Latham and Shadwell might be conjuring up, he’s able to summon a reverb unit to give his voice that extra polish. Tom’s rebirth is the highlight of the film, as he literally bursts out of the ground on his bike (don’t think too hard about it…) to claim his first victim, the ever-lugubrious Roy Evans.

Tom persuades the rest of the gang to follow suit (Hinkey doesn’t believe enough and doesn’t make it) and the sequences of the gang finding inventive ways to kill themselves is genuinely hilarious. But Abby is too scared and, unknown to Tom and the rest, hasn’t gone through with the suicide pact. Just as you think that the film has reached peak batshit craziness, Robert Hardy turns up as Chief Inspector Hesseltine, sporting a Yorkshire accent and fulfilling his usual brief of chewing whatever scenery is left unscathed by the mayhem elsewhere.

He tries to trap the gang, who have killed a truck driver, hared around the countryside and gone back to that shopping centre for more mischief (they really are very childish, though this time Jane does appear to at least badly injure, at worst kill an infant) while Mrs Latham becomes increasingly uneasy about her son’s errant behaviour and plans to break her deal with the Devil with devastating results for just about everyone.

Psychomania is the sort of film where you genuinely wonder what anyone involved was thinking (composer John Cameron comes out of it all the best – his fuzz-guitar heavy, prog rock inflected score is terrific). As noted, if you approach it as a comedy, it works wonderfully, from the stupid antics of the gang (one of them weighs himself down with so many chains and weights before jumping into the river that he can barely walk) to the typically over-enthusiastic turn from Hardy. Reid wanders through it all like she has no idea what’s actually going on and shortly after completing the film, Sanders retired to a hotel room in hotel in Castelldefels, near Barcelona, wrote a note (“Dear World, I am leaving because I am bored. I feel I have lived long enough. I am leaving you with your worries in this sweet cesspool. Good luck.”) and swallowed the contents of five bottles of barbiturates, dying from cardiac arrest two days later.

In a 2010 interview with Rue Morgue magazine, Henson, a keen motorcyclist, revealed that he was lured to the project by the promise of the script’s opening line that read “Eight Chopped Hog Harley Davidsons crest the brow of a hill.” He was devastated when he turned dup to find that the gang were furnished with common-or-garden second (possibly third) hand 350 AJS’ and Matchless BSAs that required constant mechanical attention to keep them up and running. At least he gets some wildly silly dialogue to share with sanders (Tom: “She’s dead, Shadwell!” Shadwell: “You must be very happy sir….”) and seems to be having some fun during production and Larkin, also talking to Rue Morgue, was obviously aware of what she was getting into: “It’s such an appalling concept, isn’t it?” she said. “You nearly can’t take it seriously.”

And she’s right. You can’t and nor should you even try. Any film that features dead cops in mortuary cabinets still in uniform, complete with helmets clearly isn’t taking itself very seriously so why should we. And on that level, despite all its shortcomings, it works very well indeed, a riotous, stupid but immensely enjoyable bit of old tat that’s certainly something of a one-off. And for that we should, perhaps, be very grateful indeed.