Halfway through this interview, Gavin Coates told me he doesn't like being called a greenie or an environmentalist. If you recognise his name, however, it's probably because of his children's books, which are concerned with trees, dolphins and the increasing muckiness of our planet. One of them is called The Search For Earthy's Best Friend, and he has just launched Earthy as a soft toy, which is available at a Bookazine near you and at most of the season's Christmas fairs.

Such interests sounded pretty environmental to me, but Coates, who is a scrupulous man, said, 'I love the environment but I'm not consistent. I can still eat a steak and kidney pie, drink 15 pints and smoke a few cigarettes.' Earthy, indeed, was conceived some years ago at that unecological sanctum, the bar of the Foreign Correspondents' Club, while Coates was having a drink with a man called Brian Jeffries. 'He's just died and I'm so upset, I really wanted to show him the result of our conversation, if that's the right word. Our mutually unintelligible communication. The idea came that night and I went back home and made the original Earthy for Thomas out of a cushion.' Thomas is Coates' nine-year-old son who lives with him on Lantau; his marriage to Thomas' mother, who is Zambian, ended in 1993. Coates remarked, diffidently, that he didn't really think it was fair to talk about the marriage in public, but he's voluble about fatherhood. 'It doesn't stop being terrifying. It's one of those things that's the stuff of life - it traumatises you and it delights you. And I'm sure I do the same to him.' Interviews, by their nature, make people introspective, but Coates (who is not related to Myself A Mandarin Austin Coates) seems particularly aware of the differences between his upbringing and that of his son's. Maybe that's why he portrays a precious, precarious idyll in his books, for his childhood was evidently not one of sunny expanses and abundant fruition. At one point, as we sat next to the beach at Mui Wo on a perfect Hong Kong autumn morning, he was moved to observe, 'Frankly, I wish I'd been brought up here and not in south London.' He was born in Whitechapel 42 years ago and raised in Dulwich, 'places for which I never felt the slightest affinity'. For his first 17 years, until he had a corneal graft on his left eye, he had a squint; for the first 20 years, he also had a 'diabolical' stammer. 'I was a social outcast in my teens,' he said simply. 'I was a non-person, a non-existent thing. That colours your attitudes in some ways, it makes you pretty resilient to other people's comments about you. And it makes you very introspective, obviously, because you've got nowhere else to go.' Having little contact with human beings, therefore, he drew plants and trees, and decided to study landscape architecture at Leeds Polytechnic. While he was there, still vocally fettered, he volunteered to give a presentation to several hundred people. 'I knew I'd never speak again or vanquish this thing. I was sweating buckets, weeping with terror. I'd written down four or five salient points but the piece of paper liquefied into a grey pulp, dribbling down my arm, at which point I felt I'd been dropped off the Empire State Building. And then I started to talk ... and it all shot out of my mouth, floods of words, I was blabbering 19 to the dozen, I couldn't stop. Eventually someone had to take me off the stage.' For the record, he has a particularly pleasant speaking voice and he told this rite-of-passage story with many amusing gestures (the hall of agog faces, the horror, the splurge of speech, the hysterical relief), which made it seem significant but not portentous. And now? 'Occasionally, I still stammer if I'm tired or depressed but basically I've broken the back of it.' He still had to deal with the grisly British climate, and after the coldest winter for almost 20 years - ice formed on the inside of his Victorian bedsit's windows - he fled to Hong Kong, arriving on May 5, 1982. I remarked that expatriates almost always know the exact date of arrival here and he replied, 'Well, it's a life-changing moment, isn't it?' It was a landscape-changing moment for Hong Kong: the Coates imprint may be found in Tseung Kwan O ('all my babies are the trees around the tunnel portals'), the banyan tree in Pacific Place ('I was involved in the technical side of looking after it') and the design of the waterfall you can walk behind in Hong Kong Park. Then he realised he was tired of working in an office, moved to Lamma, and became a cartoonist.

Coates is the first to admit that, as career leaps go, his has not proved wildly lucrative. 'I've chosen a route which is much less financially secure so far, but here we are, with the wind blowing through the casuarinas, and Thomas has been brought up in this bloody beautiful place.' He knows, of course, the names of every tree; when we strolled to his flat later, through fields of ginger, he pointed out orchards of peach, guava and papaya along the way. You don't have to have scraped ice off a suburban window to appreciate that such a neighbourhood, on such a day, may seem priceless.

I wanted to see the original Earthy, the product of that FCC evening, and Coates produced it from among his piles of papers and suitcases. I don't think he'll mind too much if I report that interior design is clearly not his priority. 'You go to people's houses with beautiful ornaments and think, 'What a beautiful thing, thank God I don't own it.' Outside is so lovely, I don't bother about inside too much.' Except, of course, when he's compelled to write a book. 'Sometimes people say, 'I wish I was an author, my ambition is to write a book,' and I think that's ridiculous, why not go down to the pub instead? It's hard work, thankless, lonely, and unless you hit the jackpot and become a name, you're not going to make money. On the contrary. So the only reason to write a book is because you can't help it. It's like constipation, you have to get it out.' Just as I was leaving, I asked where his inspiration came from. Coates hesitated, fidgeted, then said, 'it's made me spiritual'; he said he'd bought a Bible at the beginning of the year, but that he didn't want to be pigeonholed by that revelation. Perhaps that's also part of his aversion to being classified as a greenie: he strikes me as a man who has never developed a herd instinct. On the path back, talking about making Earthy a success, he remarked: 'It's like dealing with the stammer. You have to go out and do it yourself.'