Lunchtime at Simon Hopkinson's flat in west London, and all is calm. The asparagus is peeled, the jellied chicken sits in a glass bowl, quivering and beautiful, the pistachio ice loiters in the freezer. For those who like both to cook and to eat (the two are mutually exclusive more often than you might imagine), this is the best moment of the day: the 15-minute pause between the end of one set of rituals and the beginning of another. Time, then, for a glass of cold – but not too cold – chablis and a cigarette? Oh, yes. Why not?

Full disclosure. Simon Hopkinson is a friend of mine. I have known him since 2003, when I met the man I later married; Simon was a friend of his – they share a slightly camp fondness for humming TV theme tunes together – and, naturally, I colonised him as quickly as possible. Ordinarily I wouldn't interview a friend – it's unprofessional, not to mention awkward. But in this case I decided to make an exception. For one thing, he is a cook, not a politician. I would be asking him whether it is always necessary to skin broad beans, not how many times he has fiddled his expenses. For another, I was absolutely desperate to have lunch at his flat.

The occasion for this interview is The Good Cook, his six-part series for the BBC – which is something of a shock development, because Hopkinson is not some hot new discovery; he was born in 1954, and has a long career both as a chef and as a food writer behind him. Also, television has always been something that he claimed not to want to do. He is shy, you see, and could not stand the idea of talking away to "that black hole". So how on earth did it happen? "Well, the producers came to me, and I liked them immediately. I said: 'I just want to cook, to make all my favourite things', and they let me do that. Once I got going, I had a ball. I enjoyed myself. I still think – being pernickety – that my rice pudding came out a little more sloppy than I would have liked, but otherwise I'm genuinely happy with how it has all turned out." And is he prepared for what will happen if it is a hit? Will it bother him if people start recognising him at Sainsbury's, his basket loaded up with his favourite Fray Bentos pies? "Oh, let's not go there! I'll never go out again!"

I'm not joking about the pies. The great thing about Hoppy is that he is not a foodie. He loves food; he cares about it deeply, and spends most of his time thinking about it. But he is not "silly" about it ("silly" is one of his favourite terms of abuse). He likes gravy (as opposed to jus) and old-fashioned English lettuce (as opposed to rocket). Trends, for him, come and go, whereas a good pie, stew or roast is for life. His seriously good new book, timed to tie in with the TV series, reflects this. Yes, there are recipes for luxuriously dainty dishes such as scallop mousse with mornay sauce. But if you want to know how to make cheese and onion pie or neck of lamb stew, then he is your man.

The recipe for cheese and onion pie is his mother's. Hopkinson grew up in Bury, where his father worked as a dentist and his mother taught art at the grammar school (he has one older brother, who trained as an artist but now makes leather goods). "She'd learnt to cook from her mother. She made cheese and onion pie, rabbit pie, jugged hare, lovely braises, queeche Lorraine – that's how we used to say it – baked in a Denbyware dish. Classic things, but very good things. Dad was more experimental. He liked to make curries, and he used to go into Manchester to buy all his spices." The family always ate together, and the highlight of their week was Sunday lunch. "I loved everything about it. Hancock on the radio. The smell of the roast in the oven. Going to get the mint from the garden when it was lamb. Of course the meat was cooked for a bit longer than we would do it now."

At the age of eight he went away to become a chorister at St John's, Cambridge (followed by Trent College, near Nottingham). Was it traumatic, leaving home? "A bit, at the beginning. I think Mum cried every time, though." Luckily he took school dinners in his stride. "I ate everything, so I wasn't fussed about it. The only thing I wouldn't eat was the porridge, which was grey and slimy and disgusting." By the time he was in the fifth form, though, his sights were already set on a future in cooking; he had begun working in the kitchen of a restaurant, La Normandie, in Birtle, just outside Bury, and was determined to sign on there as an apprentice at 16. "It was a posh place: white napkins, waiters in white jackets. The chef, Yves Champeau, was very strict. I used to cry a lot." Champeau had warned Hopkinson's parents that he would be working very hard but his new charge was OK with that. Apart from anything else, it was good to be distracted. "It was very difficult at that time… you know… being gay and everything. Quite frustrating, let's put it like that. I didn't really come out until I was 26." Did he have girlfriends? "I tried to!" What did his parents say when he told them? "Mum had suspected for a while, but Dad had no idea at all. I remember that he said something when I was telling Mum, and she said: 'Oh, Bruce, you've no idea at all!' And she sort of shooed him out." But they were both great about it: loving and supportive.

In 1975, just a month before his 21st birthday, he opened his own place near Fishguard, The Shed. It had only five tables but he was off: a chef-patron at last. He moves towards a great cairn of papers by the window, from the midst of which he pulls an old menu. Among the starters are avocado and crab (at 70p) and six escargots (at 95p); and among the main courses are entrecote au poivre, at £2.45.

Lunch is served. Hopkinson picked the asparagus himself, and now serves it with butter. Cue a tiny semi-rant about asparagus. "People say British is the best, but it's down to freshness, not location. I'm sure the asparagus in California tastes just as good if it doesn't travel. I mean, what does Alice Waters do for asparagus? She buys local asparagus, and it's delicious." Then silence falls, and we both slurp away.

After this he bounces back into the kitchen for the second course. What's his kitchen like? It's small, nothing fancy – he has always prided himself on being able to cook anywhere. Next, we are having cold jellied chicken with tarragon, boiled potatoes and broad beans. He loves hot and cold foods together. "One of my favourite lunches is really good toasted sourdough, well-buttered, with wave upon wave of finely sliced parma ham on top of it. Or cold ham, egg and chips. Can you beat that? No." Another brief silence. Oh dear God. The chicken is delicious. I could eat it every day for a month and not mind.

He ran The Shed for two years, until he could bear the gruesome winter evenings no longer, at which point he went into Fishguard and ran a restaurant above a pub which he called Hoppy's. It was there that he won his first Egon Ronay star. "But I didn't get on as well as I should with the owner of the pub, and I wanted to run away to London – for obvious reasons." So he became an Egon Ronay inspector and spent three years motoring around the country, eating, which was heaven but not terribly good for his figure: "When I reached 16 stone, I had to stop." There followed a long stint as a private chef in Chelsea until, in 1983, he opened his first London restaurant, Hilaire.

Everyone loved Hilaire, not least Terence Conran, who sometimes came in twice a week. When Conran and Paul Hamlyn bought the old Michelin building on Fulham Road with a view to turning it into a fine restaurant, they asked him to be its chef. Bibendum was critically acclaimed, popular and glamorous. "Yes, it was quite glamorous. One of my best trios [of diners] was Alan Bennett, Alec Guinness and Lauren Bacall." Also among his customers was Elizabeth David, with whom he became friends towards the end of her life. "She didn't cook for me. She wasn't really up to it by then. We used to drink wine and eat Rokka cheese biscuits: her favourites."

It's often said that Hopkinson's career as a chef came to an end in 1994, when he had some kind of breakdown. But this is not, he says, strictly accurate. "It's true that I burst into tears," he says. "But I'd already told Terence and Paul that I wanted to go. Roast Chicken [his first cookbook] had come out, and I liked writing. I was unhappy. I wanted to write and cook nice things. I didn't want to do that manic service any more. I told them in July, and then in November I had that terrible evening. A head waiter was goading me. Bookings had been taken indiscriminately. We did something like 90 covers in an hour and a half. I just lost it, and I crumpled. Alain Ducasse was in. He wanted the recipe for my steamed ginger pudding, and to see the kitchen, and I said no to both. I went into the office and I blubbed for about half an hour and then I got back on the horse." He finally left that New Year's Eve, though he is still a partner and, thanks to this, certain dishes are unlikely ever to leave Bibendum's menu: steak au poivre, roast chicken, roast beef on Sundays, snails, fish soup and chocolate ice cream.

So he retired to a quieter kind of life. But then, in 2005, Roast Chicken and Other Stories was voted the most useful cookery book of all time. "It was thrilling," he says. "It turned my life around, because I was in the doldrums. The book hadn't earned back its advance over 11 years, and suddenly it was selling. At one point, for about a week, it outsold Harry Potter." With him firmly established as the cook's cook, subsequent books have also enjoyed good sales – though there was a small controversy when he included a non-vegetarian option in a book called The Vegetarian Option. He rolls his eyes. "Oh, people do like to be cross about things, don't they?"

The cookery book poll was excellent good luck – it was July; the newspapers jumped on it like cats on mackerel – but it was also deserved. Roast Chicken is a brilliant book. Why? Because he knows whereof he speaks. "He is the best cook," says his friend Rowley Leigh, not exactly a slouch himself in the kitchen. "His cooking is rooted in Englishness, but he's also a radical in that he looks at everything from first principles. He doesn't make prejudgments. I mean, he used to use Knorr stock cubes just because he thought they were good." Is he surprised that Hopkinson will soon be on the telly? He isn't the likeliest TV star. "Well, you could say that about [Keith] Floyd or Rick [Stein]. But if the camera gets him right, it could be fantastic." And where does Leigh stand on the great "crisp" debate? Because if there's one thing Hopkinson can't stand, it's people who use the word "crispy" when they mean "crisp"; to do so is just plain silly. "Oh, I try and toe the line on crisp," he says mildly.

Back at the table, we are now eating a delicate and exceedingly creamy pistachio ice cream. Would Hopkinson say that he is contented? "Well, I'm in a state of nerves at the moment," he says. "Worrying about the series." I mean generally. Yes, he thinks he is. He lives alone, and likes it, and his strongest feeling is that he would hate for his life to change in any way. He knows he is rather lazy, socially speaking. But he just has a great liking for home. "If no one ever phoned me, I'd never go out at all," he says. "But give me dates and I'll do it, because I do want to, really. It's like that bit in Brideshead Revisited, when Anthony Blanche first meets Charles Ryder. What does he say? 'I shall come down your burrow and ch-chivvy you out like an old st-t-toat.'"