Robbie Coltrane strides into the Ideal World offices and lights up a cigar about the size of a baby's arm, releasing a cloud of acrid cigar fumes into the previously pristine atmosphere, whilst assuring everybody that they're actually much better for you than cigarettes. "These things are just like smoking leaves," he says, waving the cigar wildly in the air. "Did you know that in Cuba, where everybody smokes cigars, they've got lower lung cancer rates than Britain? It's all the chemicals they put in that kill you."
Voluble, outspoken, a man who raely deletes his expletives, Robbie Coltrane is in Glasgow to plug his new project, the book of the Coltrane's Planes and Automobiles series.
It may have seemed a strange move at this point in his career. He began as yet another comic actor with an amusing Scots accent, but, after playing parts such as the chain-smoking, gambling Fitz in Jimmy McGovern's Cracker, not to mention his award-winning performance in John Byrne's Tutti Frutti, he's now started to move into the TV "serious performer" superleague. So why choose to do a documentary about such arcane subjects as the history of the two-stroke engine?
"You're right," he replies, "I didn't want to do a documentary now; I wanted to concentrate on my acting. In acting you get to ham it up, and be a bit wild, but in a documentary you just do your wee bit, and then stand around for two hours while the cameramen get a close-up of a spanner. But Ideal World [the company behind the C4 series] seduced me. They said things like, `We'll let you drive a Bentley around Brooklyn' and things like that, and I was hooked."
"But the origins of it go way back," he continues, "to about 20 years ago, when I wanted to write a guide to cars for my sisters, because nobody had ever bothered to explain to them how they worked. The irony is that that might seem a bit redundant now, because there's so many cars you can't do anything with. Did you know that the Japanese are planning a car where you can't open the bonnet? Sealed for life. A light will go on on the dashboard and tell you to take it to the mechanic. I think that's a terrible thing! You don't want to have to rely on a mechanic to tell you if something's wrong with your car. You don't want a cobbler to tell you if you need new shoes."
He goes on to rail about the dull way engineering is taught in schools, where kids are bored rigid by talk of Boyle's law, when they should be being told how to build a radio, or take apart a toaster. He's got a point; especially in Britain, where being interested in mechanical things is seen as the sign of a spotty nerd, who'll undoubtedly go on to bore you senseless with trainspotting stories and anecdotes about carburettors.
It all used to be so very different. In the 19th century, engineers were heroes who were going to subdue nature and help Britain conquer the world. Now it's computer programmers with ponytails who are the sexy face of technology, not sweaty guys wrestling with a gasket. As Coltrane points out, however, until we can travel to work via the Net, we're going to be stuck with engines for a bit yet. And it's the idea of bringing back the romance of big engineering projects that is really animating him just now - the chance to show that (as he puts it in the book) a diesel engine is as much a work of art as a Michelangelo.
If that's the case, then the creators of these masterpieces should be given as much artistic leeway as we normally give to great composers and the like. Talking of Whittle (inventor of the jet engine), Coltrane remarks, "He had a reputation for being difficult; but then, no wonder, after being told to sod off for most of his life. It's only the British who expect creative people to be brilliant and intelligent, but at the same time nice people, which is just, like, why? [adopting a self-important, middle- class voice] `Oh, apparently Beethoven was very rude in the newsagents.' Does it fucking matter? Have you heard his Fifth Symphony?"
It's easy to jump to the conclusion that this defence of "bad behaviour" and the hard-living, hard-talking exterior that Coltrane exhibits is a reaction against his family background. Contrary to popular belief, he actually had a conventional middle-class upbringing - dad a doctor, mother a pianist - and was sent to private school. You could say the story that developed was a conventional one; kid rebels against dad's right-wing political beliefs, and throws in the doctor's career that was waiting for him to become an actor. Maybe. But Coltrane points out that, contrary to appearances, they actually had a lot in common. "My dad went to North Africa and spent the war scraping wee boys off tanks, because it was the medic's job to get rid of the stiffs, so that the new troops wouldn't see them. The experience made him a complete humanist, I think.
"He was totally cynical about all politicians and all political systems. He was an anarchist in the true sense of the word; and I don't mean he went round in a parka spraying A on walls while no one was looking. I mean a real anarchist. But he was a Conservative with a massive C. I don't know why really. I think a lot of people came back from the war and sort of drew in all their tendrils, and just thought, `No more'."
In one respect, he isn't following in Dad's footsteps: he rails against Harriet Harman's policy on single mothers, and suspicious of the whole New Labour project. But still, with stories of jet-setting all over the world, his "very left-wing" political views might seem a bit incongruous. The projects he's working on don't seem to be encroaching on Ken Loach territory either: a new production of Vanity Fair, more film work, and a shot at directing a "very scary" horror movie.
Later on in the evening, at a book-signing in Glasgow, he chats with the public, tells jokes, does Judith Chalmer impersonations, and generally has people eating out of the palm of his hand. It's obviously good to be back on home territory (after the "snotty" reception he got in Edinburgh), and the audience laps it up. In the final analysis, it's easy to be cynical about talented guys who have had some breaks (in Scotland it's de rigueur). But the sneerers should be aware of his seriousness. As we were chatting about devolution just before I left, he concluded, "I think it's a good thing, but then I only want what's best for Scotland. That has to be the most important thing." So there.
`Coltrane's Planes and Automobiles' is on Channel 4 at 7.30 on Sundays. `Coltrane's Planes and Automobiles' by Robbie Coltrane and John Binias is published by Channel 4 Books at pounds 17.99