This week sees the release of Alex The Crow Proyas' latest film Dark City, starring Rufus Sewell, Kiefer Sutherland and William Hurt. An ambitious, futuristic fantasy with a neo-noir feel, it shows Sewell's character Murdoch begin to question the very nature of reality, as he discovers a fiendish Underworld deep below the earth, inhabited by a people known as The Strangers.

Bald-headed, chalky-white and given to collective chanting, The Strangers are ruled by a dog-collared Ian Richardson (looking for all the world like he has just escaped from an S&M old-peoples' home), who stops time each night to alter the city and its inhabitants in a process known as Tuning. When they're rumbled by Murdoch, it's up to one of their number - the silky-voiced Mr Hand - to track Murdoch down, and destroy him.

"When I went to read for the part," says Richard O'Brien, "Alex said that he wrote it with me in mind. I don't know if he was just being flattering, or diplomatic, or simply lying, but it was very nice anyway". O'Brien headed off to Australia, where Dark City was shot entirely on set, in the cavernous exhibition halls of the Sydney Showground. Dressed in the Strangers' garb of long narrow coat and fedora, O'Brien says he did begin to "melt a little" after a couple of takes, but could easily nip back to his trailer, put the air-conditioning on and cool off.

"I didn't have to work every day, of course," he continues in his charmingly polite, clipped tones. "I just had to pop in for scenes every now and again. So there were stages where I wasn't working for two weeks, but still on daily call. That meant I had to stay near the hotel, which was fine. It was a rock and roll hotel and the bar was very pleasant. I used to entertain a lot in my room. My room was always full of no-hopers and ne'er-do-wells. People would come down and see who was around. They'd say: "Well, Bon Jovi isn't in town, but that strange, skinny English geezer's there, so we'll go and get drunk in his room until six o' clock in the morning".

Since O'Brien was playing a character who was inhabiting a dead body, such antics could be counted as preparation. "It didn't really matter if I looked like death warmed up, because that was exactly what I was supposed to look like," he laughs. Still, it must be difficult to play a character leeched of all emotion?

"It's always difficult to deliver a line dispassionately. I had to try and lack any real colour and emotion, but at the same time maintain interest. So yes, it was always a bit of a struggle. What I tried to do was to keep my eyes as still as possible and as wide as possible and try and keep this kind of face that didn't move. And say the lines in a kind of way that was disembodied.

Mr Hand is just one of the infinite varieties of evil O'Brien has essayed over the years. "I've only played one goody in my entire life," admits the actor. "I did enjoy it, but I suppose it goes with what you've been given physically, protoplasmically. That's the way it works. People always say: 'It's nothing to do with looks, all to do with acting'. Well that's rubbish. It's all to do with looks. David Jason is never going to be James Bond. Here I am being rather skeletal, so consequently I get these kinds of roles."

Of course, O'Brien wrote Rocky Horror's Riff Raff for himself. Hasn't he ever been tempted to write himself a nice romantic lead? "No," counters O'Brien. "I've always known what I've been suited to, and what I've wanted to do. When I first started I wanted to do comedy and gothic horror. Rocky Horror was exactly a mixture of those two elements. Anyway, you need someone to play these kinds of roles. In my twenties I thought, Christopher Lee is getting on, Peter Cushing is getting on. Vincent Price is getting on - maybe I can slip into the gap, when they all disappear? It's a nice territory to be in, I think."

Later this year O'Brien plays another baddy in Cinderella opposite Drew Barrymore, but for now he's heading off to a retreat for 10 days "to hide away from the world and recharge the psychological batteries". Is it very remote, I ask, will he be cut off from the telephone and television?

"I do hope so," says O'Brien, "but then again, I'd have to have a telly 'cos I couldn't miss The Simpsons. I love The Simpsons. That's the funniest thing on television. It's excellent. Now, if they made a live action movie, I could play Montague Burns.

That would be rather good..." And with that he disappears, relishing the thought of his next repulsive villain.