EWEN Bremner is talking about what it feels like to be Jude Law's left buttock.
"Basically," he says, "movies come down to economics and they're always too expensive. From a producer's point of view, an actor is either going to make him money or save him money. If you're Orlando Bloom or Johnny Depp with a huge online following of girls, or boys, you're going to make him money. But once the producer's cast his star he's still got to cast 24 or maybe 124 other parts. He might say, 'I can get eight of those other guys for one Jude Law' and then he'll make his decisions. Really, the rest of us are just cheap labour."
But Bremner isn't complaining. From the moment, as Trainspotting's Spud, that the most famous job interview scene in cinema history shot him to fame, he hasn't had to worry about impressing a room full of stern-faced men in suits, like the rest of us doing normal jobs. The Edinburgh pub where we meet - a short distance from where Irvine Welsh's junkies bounced off a car bonnet in the opening shot - may be deep in gloomy contemplation about a bread-and-water Budget and tough times ahead, but there will probably always be films, and they will probably always need characterful types like Bremner to make the leading man appear funnier or cleverer or more chiselled.
Bremner has just finished a turn on the new Woody Allen movie, You Will Meet A Tall Dark Stranger. "I'm Josh Brolin's friend, a reclusive writer," he says over his afternoon cuppa. At 38, he's been doing this kind of thing for so long that he can now play dads. (Spud a dad? I know, it takes some getting used to). In Dive, marking his return to telly drama, he's the father of a schoolgirl diver who's training for Olympic glory until she falls pregnant.
Both are support roles but it's surely better to be small for a legend or an exciting talent than big for a fool. Stranger is Bremner's second Allen movie. "Woody's sense of humour is completely intact and unique," he says. "He's no luvvy extrovert and very quiet but he knows what he wants, chases spontaneity in every scene and gives his actors tremendous freedom." And Dive, a two-parter for the BBC, is written and directed by Dominic Savage, the Stanley Kubrick protege and double Bafta winner whose previous work Freefall focused on the banking crisis.
Bremner is fascinated by stage mums, touchline dads and hothoused kids. "My daughter Harmony is ten, younger than Lindsey in the drama, and she's got her passions too, so as her dad I want to encourage them.
But in a pressure-cooked environment like diving - and I've seen this in acting as well - how much is it about the kid's ambition and how much the parents'? As parents I think we're always novices, and every day presents a new challenge."
The son of Edinburgh art teachers, Bremner was 12 when a Harold Pinter play on the box got him excited about acting. He quickly worked out what Movieland wanted from him. "I play the other guy or the guy's friend," he said a few years back. "The strange guy, the mysterious guy or one of the guys, but not The Guy." But The Guys - Schwarzenegger, Stallone, Christopher Walken - were actually GUYS, as big as stars got, and so were the films: Pearl Harbor, Black Hawk Down and Alien vs Predator.
He must have some stories to tell. "I couldn't tell you any about Walken without then finding members of my family carved up," he laughs. "Terrific actor, though." I'm more interested in what the superstars thought of the boy from Portobello. "Well, I don't think Sly would remember me. The stars will either dig you or they won't. I remember getting treated like shit by a big boots actor until he found out I'd worked with Mike Leigh (on Naked]. Suddenly he was my best friend."
Bremner says he understands Hollywood better than when he was young, ambitious - and terribly fussy. "I was a real snob about the films I would and wouldn't do." So what was the one that got away? "Boogie Nights. I never returned (director] Paul Thomas Anderson's calls. His people would be like: 'Paul really loves you, there's a great part here for you.' But I thought the script was too sentimental. Of course, when I saw the film I was kicking myself.
"Back then I was a disaster zone about my choices. I turned down plenty of films which proved to be hugely successful. And, of course, I've also had plenty of experiences where everyone thought we were doing brilliant work and it ended up pretty horrific. Same as any actor really."
The biggest disaster of all would have been to pass on Trainspotting, and Bremner almost did that. "I'd been in the play, and the screenplay didn't seem to have the integrity of the book - it was too pop-friendly, with designer junkies. Plus, having played Renton onstage I was a bit aggrieved not to be considered for the role in the film. I was just being a stupid snob again. But I'm so pleased to have done it and I still love it."
Bremner has been back living in Edinburgh for a while - his partner is the jazz singer Niki King - and the most asked question when he's spotted in its streets is: "Are you doing Porno?" He's up for doing the sequel and at one time it was reckoned that all of the central players were, apart from Ewan McGregor. "I don't know," he says. "I worked with Ewan last year but we didn't discuss it. We were young when we made Trainspotting and I'm sure the other guys are as grateful as I am for having been involved. I've had a fantastic time in this crazy industry and I've been very lucky."
Hopefully, the likes of Jude Law are just as grateful to the Ewen Bremners.
Dive is on BBC2 on Thursday and Friday at 9pm
• This article was first published in Scotland on Sunday, 4 July, 2010..