Some movies manage to transcend a barking plot, a cast of talentless no-hopers and dimwitted dialogue to achieve a bizarrely compelling alchemy.

Chemical Wedding is such a half-baked achievement. It's a hare-brained marriage of bargain-basement sci-fi, occult tomfoolery and softcore sexual absurdity. With Simon Callow in a velvet suit and matching titfer, natch.

He plays Professor Haddo, a stammering Cambridge classics professor in a funny wig who appears to have escaped off the set of Little Britain.

For some reason, a small group of spotty university scientists are experimenting with a virtual reality suit and the legendary Z93 supercomputer.

However, one of the boffins - Dr Victor Neuman (Jud Charlton) - is a follower of Aleister Crowley - "the wickedest man in the world" - and has loaded up the hard drive with black magic software.

Mild-mannered Haddo is coerced into the suit and - knock me down with a voodoo doll - emerges shorn, his stutter replaced with a steady stream of blasphemy. And a fancy for peeing on his students.

But that's not all. Badness me no. He's also got a taste for orgies above hippy trinket shops and ultimately fancies getting hitched to a redheaded "scarlet woman" in a diabolic chemical wedding.

The script - scrawled by Iron Maiden frontman Bruce Dickinson - is so comically dire that he should be locked in one of the devices from which his band takes its name.

"Have we met?" some well-meaning don inquires of Haddo, only for the loquacious Callow to reply: "Only on the Astral Plane".

It's contrived New Age bunkum...but delivered with such jawdropping conviction that you find yourself entranced as if watching a train collision in slow motion.

This is the sort of camply preposterous nonsense where semen can inexplicably be delivered by fax and a wheelchair-bound codger with an electronic voice box gets the job of delivering the exposition. For ten minutes.

There's no attempt to rein in Callow - a lumbering hybrid of George Melly and Buddha - and he boisterously runs riot in a performance that has more ham than Porkinsons' factory.

Yet you will never be bored. So utterly doolally is this mincing extravaganza, that resistance is futile. Guilty pleasure of the year.

Tim Evans