A big star, but shrinking: For a while, Robbie Coltrane put on a stone a year. The comedy and the fat seemed inseparable. Now he's got a new wife, baby, house, diet, are we going to see the emergence of a sensitive soul?

ROBBIE COLTRANE, a little under 20 stone, delicately shuffles up the stairs and into the Bafta cinema in Piccadilly. He's been dieting. From a distance of 15 feet, he looks fat, hugely fat, but there's something about his fatness that's not horrible - he's strangely shapely, as if he's supposed to look like this - supposed, for instance, to have this vast, rippling face, to have this belly which looks, not like a piece of surplus flesh, but something integral. His head looks perched on top of the rest of him; his fingers are very long, very thick, and covered in motor oil. He's flown down from Scotland, but not before digging around the engine of a 1950s car; you wonder if he's left his hands this dirty to create a conversation-piece. He wears: a black suit with narrow lapels, white shirt, jazzy tie, leopardette brothel-creepers.

This is an important occasion for the Scottish comedian, who is being lionised like never before: today, the ITV company Meridian has organised a press-conference, buffet lunch, and cinema viewing, no less, of Coltrane's current series Coltrane in a Cadillac, in which he is filmed driving across America.

The lights go down. The show, energised by frequent bouts of rock music, is not quite a comedy, not quite a documentary.

It's slightly more about Coltrane than it is about America.

At the beginning, Coltrane is filmed going to various classic car dealerships in Los Angeles; when the dealers give him their patter, he looks at the camera and makes a face. When one dealer is out of earshot, he says: 'Everything's painted the colour of a tart's handbag]'

In the cinema, the critics laugh. The story continues. Coltrane makes his way across America, being quite patronising, quite funny but not very, and loving himself. He drives through Los Angeles, shouting: 'Louise, you were fabulous, fabulous]' and 'George, loved your picture]' at pedestrians, in an American accent. Then he drives out of town and into the desert, where he tells us, in a prim English accent, how he thinks the quality press will respond to the series: 'Whilst it might be some people's idea of ideal television to watch the rather enormous Mr Coltrane driving an old banger across the salt flats, I found myself getting up to make a cup of tea after only 10 minutes.' And you can sense that part of him, out there in the middle of nowhere driving his 20-odd stone along in a 1951 Cadillac, believes that this view, however ironic, might be too close to the truth for comfort.

After two half-hour episodes, Coltrane meets the British press. He sits at a table, smoking an Embassy Regal every eight minutes, tapping his brothel-creepers on the floor, drinking a lot of coffee. He's playing the part of the Glasgow lad, the raunchy car-buff. 'Yes,' he says, in a gruff Glasgow rasp, 'I've been under the bonnet.'

He looks at his oily fingers. He keeps tilting his head up and raising his eyebrows; when he does this, everyone laughs. He's got a fine sense of timing, of what this audience wants. When someone asks him exactly what he was doing under the bonnet of a car, he says, smiling: 'Well, if you really want to know . . .' and goes off on a long, detailed explanation, talking about gaskets and firing pins, getting down to micro-details of how these things are different on cars from the Fifties.

Coltrane says: 'What I don't like about modern cars is that they're a miracle of engineering, but when you're driving one, you could be watching a video.'

A journalist says: 'Why a Cadillac? Why not a Chevrolet or an Oldsmobile?' Coltrane: 'Are you having a breakdown?'

Journalist: 'But . . . what's so good about a Cadillac?'

Coltrane: 'I love Cadillacs. They're real white trash cars. The Packard was always their Rolls-Royce, but the Cadillac was always the first car blues singers would get when they got their first hit album.'

Next, the buffet lunch, in which Coltrane sits at a huge oval table. About 20 journalists sit at the same table. Coltrane tells joke after joke: people swing their heads back with laughter every couple of minutes. After he has told a joke or an anecdote, he'll often hang his head, pause, and then bring his head back up and raise his eyebrows, milking a second laugh. He says: 'I used to work with this guy, he wore these . . . gothic clothes. Black suit, black tie, black cape, he had this pale face. And then, one day, he comes into work, and he's wearing . . . you know, ordinary clothes. So I say: 'What's the matter, has somebody died?' ' Everybody laughs. Coltrane says: 'And . . . he didn't get it. He didn't get it]' Everybody laughs again. Coltrane hangs his head. Five seconds later come the eyebrows.

He has only granted one interview, which is mine. After an hour of making people laugh, he comes up to me with his publicist and shakes my hand, looking weary, all laughed out. On the way up the stairs, he says to his publicist: 'Well, that wasn't too bad. Nothing about the weight, and nothing about the baby.'

We sit down. I say: 'Two things first of all, Robbie - the weight, and the baby.'

He looks at me filthily. 'Ha ha.'

'Right. Well. Hello. Anyway, interesting show, and . . . I'd like to talk about, you know, how you came to be the figure you are now. I mean, when did you first think of yourself as a performer?'

'Oh, come on. That's all documented. That's all old stuff. Early Seventies, I suppose. Mid-Seventies, I suppose. Come on, this is old stuff. No, that's been in so many interviews. I did all that stuff about 10 years ago.'

'So you won't . . .'

'Well, I mean there's no point in going over old ground. People get fed up with all that early origins stuff. I certainly do.'

'But, say, your schooldays? Can't you . . .'

'Not really. It's all been done to death really.'

'What will you talk about?'

'Well, the series. I'm only doing this for the series.'

He sits there, black oily fingers, vast belly, suit fitting him like a burst condom, a face that Angela Levin described in the Mail on Sunday as a 'child's sponge birthday cake', stupid shoes.

'So - are these clothes in character for the television series? I mean, are you wearing these particular shoes because they're Fifties shoes?'

'You cheeky bugger.'

'Well . . .'

'No, this is how I dress normally.' Looking at me. 'Well, I wouldn't walk around looking like a fucking student at your age. Cheeky bugger] I wouldn't] Who wants to be thought of as a student? God]'

There are lots of things you wonder about Coltrane. For instance, why did he get so fat? He has said that, for several years in the 1980s - this is the era that his friends and colleagues refer to, gingerly, as the 'hell-raising years' - he put on a stone a year.

Coltrane has developed a very left-wing public persona, very man of the people; in 1985, he refused to bow to Princess Anne at the Royal Variety Performance. But he's also incredibly grand, with a big house, lots of land, seven or eight cars, and a boat. And he advertises Persil, which, he told the journalist Tom Hibbert, 'is very good. In fact, it's so good that a month after we brought it out, Fairy had to go and reformulate their stuff.' We?

And he's always been posh, having been educated at Glenalmond, often referred to as the 'Eton of Scotland'. So how real is his thick Glaswegian accent?

And: why does such a talented man need to do so much work, so tirelessly - why does he drive himself so much? He does television, terrible movies, ads, stage plays, documentaries; he does comedy and straight roles, anything, everywhere: is he searching for his true identity as a performer?

In the past few months he's done the Cadillac series and the book (Fourth Estate, pounds 9.99) that goes with it, a television film called Johnson and Boswell, a cameo role in the Hollywood picture Huckleberry Finn for Disney, several Comic Strip films, one of which he wrote and directed; in a couple of weeks he's going to play a starring role in Granada's Cracker, a series about a criminal psychologist. He once said: 'Brando always said that no moment in front of the lens is wasted - and that's absolutely true.'

Sitting there chain-smoking in his nightmarish leopardette crepe shoes, Coltrane's being incredibly grand, as if this is how he thinks a big star should act - patronising, dismissive, unwilling to do anything but give pat answers; he looks slightly piqued to be wasting his time not being flattered by several people at once.

This is Coltrane at an awkward point in his career; the days of being the fat cult comic who's chummy with journalists are over, and he hasn't quite formulated a way of acting like a star. As a star, he's all over the place.

'What made you do the Cadillac series?'

'Driving across America - it was just something I always wanted to do, I don't know why. It would have been easier and quicker without a film crew, obviously. But it occurred to me, I didn't really have the time to do it, and I wouldn't have done it on my own because of my commitments with work. I thought it would be a good idea to combine the two.'

'But why couldn't you have just . . . had a holiday?'

'Cos it would mean missing work. It would mean missing . . . well, I would have missed that Disney movie, which I enjoyed immensely. Working with Jason Robards, for God's sake]'

'Do you feel that you have to keep on the move? That you always have to be working?'

'Yeah, you do. You have to keep doing things that interest you, really. And excite you, and bring out the best in you . . .'

Coltrane goes off on a long, windy spiel of luvvy-talk, something which he does all the time, if you don't pin him down quickly. He covers the same circuit several times in our 45 minutes, gushing fairly unconvincingly about all of life being the same, really, and then, contradictorily, about how he feels lucky to be a performer, and then about how bad life can be as a performer. 'It's a life which is slightly larger than life,' he says. 'The bad points about it are much bigger than most people's bad points.'

Coltrane perpetually looks as if he doesn't know what tone to take, how to present himself. Throughout the interview, he's on edge; if you take him seriously for a while, he'll suddenly change the subject. He says, of a photograph on the wall 'That's Susannah York up there, isn't it? Look, she looks just like Harry Enfield there, doesn't she? Oh, but she's a stunningly beautiful woman. Gorgeous.'

We talk about Coltrane's huge range of hobbies. When he isn't working, or desperately trying to get work, he: restores classic cars, he's designing a racing car ('Just a wee racer; it'll look probably like a wasp with four wheels on it, with a wasp tail on it'), he goes about his local loch in a boat, he's a serious artist, he's restoring 'an American space-gun', he's designing the interior of his house so that it looks like a ship. A friend of his told me he'd recently made a successful auction bid for some wood panelling from the Titanic's sister ship.

'I just regard myself as a creative person, and I like making things, I really do,' he says. 'It may sound pretentious, but when I was a young man, I thought I was a painter, and, you know, I could go back to that tomorrow if I had to.'

And then he's off again, ranting about how he prefers the atmosphere of movies to that of the theatre: 'The theatre is very middle-class, it's full of lots of middle-class people talking about getting in touch with their feelings, and all very intense, whereas on a film set, it's predominantly workmen, it's predominantly tradesmen, it's predominantly sparks and chippies; it's a much more natural mix of people. 'Cos you've got your arty- farties, and you've got guys who are lugging great lumps of equipment about . . .'

This goes on and on, Coltrane weighing up both sides of the argument at length, and then coming down heavily on the side of the guys who lug the lumps of equipment about. By the end, he's in cockney, saying: 'Lo's o' pee-poo taw'in abaht veir noo mo'or' - although, of course, he's an arch arty-farty himself.

What other kind of person would say: 'When I was doing Mistero Buffo, some nights, when it was really hot, and the audience was hot, and you'd just think, 'Yeah] This is it] This is absolutely . . . it]' And you stop questioning all the other possibilities about what might be wrong, and you just get the notion that you're following some irresistible path . . .'? He then hesitates for a moment, and says: 'But that's true of most things. It would be true if you were a cook or something like that.'

Three years ago, Robbie Coltrane moved back to Scotland with his 19-year-old girlfriend - now his wife - Rhona Gemmill, who is a sculptress. They have a four-month-old child, Spencer, named after Spencer Tracy. The move was an important part of a pattern - Coltrane is actively trying to change his life, one big step at a time. First, he got a steady girlfriend. Next, he left London and the 'hell-raising years' behind, bought an old barn north of Glasgow, and began to convert it. Right now, he's on a strict diet, and he's teetotal. After that, he plans to give up smoking.

He lights another Regal. 'I've lost four stone.'

'Four stone? How?'

'Just by being on a horrendous diet. I don't eat any fat, don't eat any bread. Just eat the occasional baked potato. I do it all through Nutri-System. You pay the money, they give you the grub. And they say: If you eat no more than this, you will lose 7lb a week. They send you the food; it's like aircraft food, or those Marks and Spencer meals you get, in the wee trays.'

'What about exercise?'

'I'm still too overweight to do any serious exercise without damaging my heart. Once I've lost another three stone I'll go back and do some boxing training.'

Go back? Yes, Coltrane boxed when he was at prep school in Scotland, just as he boxed a little at the age of 18. But in his early teens, the first years at Glenalmond, he seems to have been chubby, unsporting, not happy; this is when, some of his schoolfriends say, he became interested in being funny. When I asked him if he'd liked Glenalmond, he said, without hesitation: 'No] I hated it]'

The son of a forensic surgeon and a pianist, Robbie MacMillan was born in Glasgow in 1950. After a childhood he has been keen to describe as 'not spoilt', he was sent away to Glenalmond, in Perthshire, at the age of 13. Euan Kerr, his first friend at Glenalmond, says of the 13-year-old MacMillan (in a posh Scottish accent, like an Etonian with differently fluted vowels): 'He was phenomenally keen on lorries - he used to pretend to be a lorry. He knew all the makes, where they went, everything about them. He had a very enquiring, curious mind.'

The young MacMillan - 'Fat Rabb' says Kerr, 'he probably christened himself that' - was bright, witty, a bit of an oddball, and plump. 'He was . . . chubby,' says Kerr, still a friend of Coltrane. 'He was the classic chubby young boy. He was the fat boy who started telling jokes to protect himself.'

'He could be both melancholy and happy,' says Alex Grieve, another contemporary. 'He wasn't conformist, although he wasn't the most rebellious boy, by any means. When he was in charge of the junior dormitory, he used to rule it with a fairly good rod of iron.'

Coltrane's schooldays sound as if they were intense, mildly prankish, and a trial to him, offset by a few glorious moments on stage, in revues, making people laugh. One contemporary describes him (another posh accent) as 'a bit weird.' Once, he stole the gowns from various prefects and hung them on the clock tower. In his last year, he got 'reasonably fit', and won a place in the First XV, as tight-head prop.

'I think I was very good,' he tells me. I was never a great ball-skills man, but it was great. But then, when I went to art school, and I had my hair down to my arse, the idea of wandering around with people in short hair and sheepskin jackets . . .'

And so began the unhealthy years, the years of drinking and eating and drugs, the years of 'getting pissed and feeling people's arses', as he has put it. Coltrane has always attracted lots of women. As his friend John Sessions puts it: 'Ladies don't like what we think they like.'

First, Coltrane thought he might be a serious artist.

At Glasgow School of Art, he painted 'portraits, which I was never very good at, but I had it in my head, somehow, that you had to be good at portraits to be a great artist.'

'A . . . great artist?'

'Yes, I wanted to be Rembrandt, and then I wanted to be Brando. Neither has happened, so there you go.' Acting 'did unleash something in me. I got the acting prize at school and all that. But I got the art prize as well, so it was always a toss-up which to do, really.'

He spent the early Seventies doing various things - training to be a teacher, travelling, rebuilding classic cars. Then he made a documentary about Glasgow gangs, called Young Mental Classroom. In 1976, his sister, a student at York, died. Coltrane told GQ magazine: 'I don't fucking know why she died.'

He'd pursued his interest in acting at art school, and, after he left, he got a part in a play in a small theatre - it was The Slab Boys by John Byrne, a brilliant trilogy of plays about three foul- mouthed Glaswegian boys. That was it. He changed his name to Coltrane, after the saxophonist, and became a straight actor for a while, getting a few parts here and there, came to London at the turn of the Eighties, and became known, relatively late, as part of the generation of comedians which includes Ben Elton, Stephen Fry, John Sessions, Rik Mayall, and Adrian Edmondson. In 1985, he got a small part as a mechanic in Mona Lisa, and, best of all, in 1986 he played Danny McGlone in John Byrne's television series Tutti Frutti.

And he put on a stone a year. John Sessions had told GQ: 'Robbie has a strong self-destruct streak . . . a deep, driving melancholy.' Sessions told me: 'He certainly had.'

'Why?'

'I can think of several reasons for that, but I don't think I'll go into them.' Later, Sessions said: 'I don't think he liked himself very much; that made him do it. He reconciled himself to the fact that he was going to get bigger and bigger and die; there was something in there - he couldn't find the right lady.'

'That's the reason?'

'I can't go into them - they're very personal things that Robbie would not thank me for talking about.'

So, Coltrane's girth grew with his success. Try to imagine his state of mind: he was a fat Scot, a talented comic, great company, good at making people laugh, displaced in London, not quite belonging, but a member of this comic troupe, this generation of comics. He was the fat one, the uncompromising, hell-raising, funny one. He had problems. You can just about see it, can't you: bingeing and boozing - and getting fatter - was his way of hardening his identity, and it was also a way of comforting himself; a poisonous combination. You can see, too, how it must have almost become his life, this business of getting fat, how it must have entwined itself with the rest of him. 'I think he believed that, somehow, it was part and parcel of what sold him,' says Sessions. 'But now he's realised that people like him because he's funny.'

AND Robbie Coltrane is funny. He can put on practically any accent you care to name, and jumps into it with a manic enthusiasm which is rather charming - he's leaping from: 'Honey, why don't you get your black ass into this room now]' (Southern black woman), to Manchester, Birmingham, the Lichfield of Dr Johnson, which he's just been doing, to the combination of Glasgow and Manchester he plans to use for Cracker.

He's lost four stone, he's a success, he's cleaned up his life, he's unsure of himself in a profound way, and he smokes constantly. Embassy Regal as well.

'I smoke Regals because they're very strong,' he says. 'The king-size ones aren't really as good as the little ones; the tobacco's packed in quite a different way . . . I smoke Majors when I have them. I used to smoke Player's Navy Cut tipped. People like to kid themselves on and smoke these tampons, these fuckin' things wi' holes in the filters . . .'

Coltrane lights another Regal. He smokes like an old man, quite automatically, with no showiness, no posturing. He says: 'There's no point in being noncy about it - if you smoke, you're doing yourself no good. But I will give up. I'll give up when I've lost the weight.'

What next? Well, after his work with Jason Robards in Huckleberry Finn, he says, there have been lots of movie offers. Also, he's just directed a Comic Strip film, 'Jealousy', and is keen on directing, although nothing with too big a budget. 'The bits that work best,' he says of 'Jealousy', 'are the ones that are exactly like what was going on in my head, which means that I can do it . . . some directors, what's wrong with them is that what's going on in their head isn't very good.' And he's polishing up his Glasgow/Manchester accent for Cracker.

'What's your real accent?'

Coltrane ponders. He sits there, great thick hands on his great thick thighs. 'I tend to pick up the accent of wherever I am, just for the sake of social ease,' he says, in his rough, stage Glasgow accent. That's where he still is - in the notional Glasgow, the Glasgow that exists in the minds of casting agents, film producers. It will be interesting to see how he turns out, when he gets thin.

(Photographs omitted)