The menu for Rowley Leigh's big new restaurant, Le Café Anglais, is about the most alluring document I have ever seen. It would not be a lie to say that I've spent more time mooning over it than I did in studying the brochure for the hotel where I spent my honeymoon. Ditto the new Vogue, and the Lakeland Christmas catalogue. Admittedly, my version is an early prototype, printed for me from a machine in Leigh's study in his Edwardian house in Shepherd's Bush, and since he was then (this is a few weeks ago, now) obsessively rewriting it almost every day, be warned: some details may have changed. But the bones of it - its superbly refined scope, its challenging clarity - will not waver, except according to season. As his friend Simon Hopkinson says, Leigh is one of the best cooks we have: like me, Hopkinson would cross London to eat one of his omelettes ('he is the greatest omelette-maker'). But for these dishes, I'd cross the country. More to the point, I would brave Whiteley's, the horrible Bayswater shopping centre (where his new restaurant is to be found) with its tatty Starbucks, recirculated air and humming escalators. Lately, when I picture Whiteley's, I find myself thinking: Yum. Parma ham with pickled damsons! Pike boudin with lobster sauce!

In fact, you don't have to cross Whiteley's threshold to make your way to the lovely Art Deco room - formerly McDonald's - that houses the restaurant. It has its own street-level entrance. It also has a long bar, an open kitchen, a giant rotisserie, huge windows and a ceiling so high that small birds could fly around up there and not much bother the sybarites below. And the menu? Oh, it's clever: prescriptive, but not stern (though the pudding list - fruit, ice cream, rice pudding, yoghurt - may be a little ascetic for some). Best of all, like the restaurant that made Leigh's name, Kensington Place, it is fairly priced. It begins with hors d'oeuvres, at £3, or £8.50 for three: mackerel teriyaki, rabbit rillettes, salsify fritters, and the return of a Kensington Place favourite: red pepper, anchovies and egg mimosa (according to Hopkinson, the 'perfect balance of flavours and textures'). From here, we move to bigger plates: veal tartare, smoked eel, pike boudin (to which I say once again: yes, please). Finally, mains: grilled sole, roast chicken, partridge with cabbage. You could have the perfect lunch for under £20: an omelette with ceps and a side of curly endive will set you back £9.50, so leaving you with change for a good glass of wine.

On a crisp October morning, four weeks before the big day of his opening, Leigh, somewhat nonchalantly, shows me around. 'This is the fridge, this is for the stock and this... [reaching into a cupboard] is your lunch.' He pulls out a cloth bag from Daunt's Books, which is brimming with oranges. We go out into the street and flag a taxi that takes us to Shepherd's Bush and, on the way, we bitch about various TV chefs (he has just turned down a show - too busy and, I think, far too dignified). I love his manner: he's quite fierce and mumbling, but in a good way; he's the kind of man that you long to make laugh just to see his face transform (when he smiles, he looks amazingly boyish). Is he nervous about the new restaurant? Excited? 'Not really,' he says, with a sort of sigh. Later on, though, after a couple of glasses of burgundy, he admits that he does have one anxiety. 'There's no point in being too nervous, but I suppose I do worry that I might have lost it in terms of my pitch, in terms of knowing what people want. It used to be that what I liked was what other people liked. But I've got this guy working for me, and he's always telling me what the "young people" want. A cocktail list! Well, I don't want it full of young arseholes, choosing cocktails. I'm a proselytiser. I want to say: this is what's good. Not silly mixologists mixing drinks I disapprove of. One of my partners once said: [taste] is entirely subjective. It's not, I'm afraid. I think that there is a thing called good taste... "But perhaps people don't want to eat pike!"' He puts on an timid old lady-ish voice. 'Ooh, pike!'

Leigh lives with his second wife, Kate Chancellor (she is the sister of Anna Chancellor, the actor), their son, Sidney, and Kate's two children from her first marriage (he also has two grown-up daughters from his first marriage), in a suburban street that is straight out of Harry Potter - which is unexpected, though I've no idea why. It's very comfortable and lived-in, though I'm not keen on the sinister autodidact cat that keeps opening the drawer where its food is kept and simply helping itself (the more wine I drink, the more I expect it to turn round and speak). Leigh chucks his Guardian on the table and sets about making our lunch. Was he warned that I turn nasty if I'm not fed? Apparently not. But he finds it mystifying that a chef would meet someone at lunchtime, and then not offer them something to eat: 'It's a sign that they're detached from what they do.' Leigh is not detached from what he does, which is why, as well as being a brilliant restaurant chef, he is a great writer of recipes (he has a column in the Financial Times, and has written two books, one of which is called No Place Like Home, a title that says it all, really). Anyway, the truth is that he likes eating lunch. In the months since he left Kensington Place, he has put away a lot of lunches.

To start, we have the cheapest thing on his new menu: spaghetti cacio e pepe. It's one of those ultra-simple dishes that I would never have the courage to cook for someone else on the grounds that it might look as if I were a) very poor and b) not trying. You blanch the pasta in boiling water, drain it and then, in a frying pan, continue to cook it using ladles of the starchy water, as if you were making risotto. This gives it a creamy quality. Then you add eight tons of pecorino and a load of freshly ground pepper and - presto! - you're in carb heaven. All the best recipes have the fewest ingredients, he says. 'The first dish I learned to cook at Le Gavroche was watercress soup: watercress, potatoes, salt, pepper.' Then we have mullet on a salad of fennel and orange. It's completely delicious. Halfway through, his wife wanders in, and starts telling me about the diet she's on, and how much weight she has lost. 'You look tiny to me,' I say. My mouth is so full, I can hardly get the words out; if I was married to Leigh, I'd be the size of a bungalow. Does she cook? 'She does puddings,' says Rowley, mouth also full. 'Sort of...' she says. 'I did. Now, I don't even help. If he's doing it, he's doing it. I don't even peel the potatoes. I'm a bit... nervous with him now. I keep asking him things. Even if he's only somewhere in the house, I just can't do it. I'm paralysed.'

Kate has got used to having him around for the past 10 months, and is worried he is about to start working 'his arse off' again, coming home in the early hours, and leaving again at the crack of dawn. Rowley, however, thinks she is fussing about nothing. For one thing, he is only in the kitchen for about a third of the time that he is in the restaurant; for another, it's no harder than any other job. 'You've still got to be awake whatever you do - moving around. It's not necessarily harder.' Will he be anxious about the reviews? Restaurants being as hyped as they are these days, the critics tend to lock on to establishments whose chefs have serious form - and Leigh has serious form - like ferrets on to a rabbit's ankle. 'No, not really,' he says. 'They can make you, but I don't think they can break you.' But this is not to say that he doesn't care. He disappears, and I can hear him truffling around in his study. When he returns, he has a faded copy of Jonathan Meades's original review of Kensington Place in the Times (it opened its wholly welcoming doors in 1987): 'This is the place, and about time, too,' wrote Meades, who knows his stuff and is kind of a tough guy to please. 'I went to King's Cross at midnight to get the paper the day it was coming out,' says Leigh. 'Now, that's a nice review. It's the best review anyone ever got from him.'

When Kensington Place opened, it was properly thrilling; no PR could have created a buzz like it. The restaurant was vast for its day - 100 covers - and very noisy, but the food was serious and, more crucially, affordable (previously, in order to eat good food, you had to sell your car first, which was why fine dining was the preserve of noisy expense-account types from the City and advertising). It was a restaurant moment. 'Oh, yes, it was exciting,' says Simon Hopkinson (his own restaurant, Bibendum, opened the same week). 'It was more democratic than us - we were a bit more luxurious - but his prices just felt so right, and you knew that he'd really thought about every dish.' Leigh invented, or at least popularised, what came to be known as Modern British Cooking, a few of his dishes - foie gras with sweetcorn pancake, scallops with pea purée - becoming London classics in the process (though Leigh has since gone off them both: 'I used to have the scallops on their own,' he says. 'The pea purée was too sweet.'). He says that he felt as if there was nothing that he couldn't put on the menu, and that this was hugely liberating. Did he feel like a revolutionary? 'Yes! And it really was!' A generation of giant restaurants followed in his wake, including those of Terence Conran. 'He was in every night taking notes, though he'd never admit it. He has to invent everything himself, even the chair.'

But all good things come to an end. He left KP 10 months ago (his share in it, now sold, was 12.5 per cent), and felt strangely unmoved by his departure. 'In a sense it was just time [to go], but I also felt that it was declining, and that I was going to be dragged down with it. The funny thing is, though I really did love the place, I didn't feel a thing. When it came to goodbye dinners and my last service, I just wanted to get it over with, actually - and I am a sentimental person, usually. I'd already left, I suppose. It was a long, slow process.' Isn't it daunting, though, starting all over again? Wouldn't he prefer to have a more proprietorial role this time around (his new partner is restaurateur Charlie McVeigh)? 'Well, I will be on the stove less. But I'm no good at just hanging around. If I wasn't engaged, I'd probably just bugger off and have a game of golf. I need to be part of it.' Besides, he still has what you might call missionary zeal. His new menu 'forces the customer into being a bit more active in choosing his food', and he admits that, in the two decades since KP opened, things have not moved on in Britain food-wise as much as he would have liked. We run through some of my favourite restaurants, and he coolly dismisses pretty much of all them: 'derivative'; 'not good enough'; 'cynical, isn't it?'; 'it's trying too hard'; 'the food doesn't make me think'.

Finally, he says: 'Where do you go for a decent steak? There's nowhere. That tells you something about England.' He had hoped that the rise of gastropubs might be a good thing, but it was not to be. 'Sloppy, self-indulgent food that's always too sweet.' As for home cooking, the number of books we all buy has no bearing on anything. 'There used to be lots of really good food shops in Soho. There aren't now. It's such a class thing. Food is the main way the middle classes articulate themselves. It's all status. The working classes buy a Porsche, the middle classes go to Waitrose and buy organic bread.' Uh oh. Don't get him started on organics. 'It's complete nonsense. What's the point of watching bugs crawl all over your vegetables?' He was recently in Stow-on-the-Wold, where he saw a sign that said: 'We now sell organic pet food'. Good grief! he thought. The world really has gone mad. I presume that the autodidact cat is also clever enough to be content with non-organic treats.

Were his parents cooks? 'My father certainly wasn't. He hated my mother's cooking. She did courgettes and avocados and things that he thought were dreadful foreign muck.' He was the third of four children; his mother was Irish by way of Manchester, his father was half-Jewish and Welsh (I think; it's all quite complicated). His parents went into business together, not terribly successfully, importing linen, and then, later, his father travelled the country selling blankets. When Leigh was 21, however, they bought a farm on the Kent/Sussex border, and he later worked for them there, which was 'not a very good idea'. He was a rebellious boy right from the start, though he has no idea why: 'I don't know what I was kicking against, because my parents were incredibly indulgent and nice.' Perhaps he was bored? He laughs. At any rate, he hated his boarding school, Clifton College, and he tried to run away and was also expelled. But this, and the fact that he passed only four O-levels, didn't stop him from winning an exhibition to Cambridge to read English. Unfortunately, this wasn't a success either. 'I thought that I'd be challenged because I was quite clever at school, but I wasn't. The English department was dreadful. The Leavisites had been thrown out and a bunch of mediocrities had taken over.' He got in with a 'political set'. So he used to sell Socialist Worker? 'Oh, I was further to the left than that. I was very, very Bolshie. I read the Situationists [the Situationist International was a group of avant-garde Marxist agitators]. I had a lilac boiler suit.' He goes off to find me a photograph of himself. Taken in 1973, he has Lennon specs and his lip is curled in a half-hearted snarl.

He didn't get his degree and, after the stint on his parents' farm, he moved to London where he tried to write an 'intellectual murder mystery'. But he rapidly ran out of money, which is how he came to get a job as a hamburger chef at the Rock Garden and this, he loved, for all that it was supposed only to be a stop-gap: 'The compulsiveness, the theatricality, the excitement. I think I have ADHD. I find it terribly hard to sit down and write.' When his chef at the Rock Garden left and re-emerged at Joe Allen, he followed him (this is where he learned to make omelettes) and then, one day, he saw an advert for the restaurant that the Roux brothers then ran in the City. He answered it and was told that he had the job until they saw his CV, at which point, he was told that there were no jobs available. 'I said that I'd given my notice, so they went: "Oh, all right then", and I started work, but of course I was winging it: these guys all had a [culinary] grammar, and I didn't know it.' He was soon fired after he 'went down like a sack of shit', but he argued his case with Albert Roux, said it wasn't about the money, that he just wanted to learn, and he was back in. He worked for the brothers for the next four years, finally becoming head chef at the City restaurant. 'It was lunchtimes only, Monday to Friday. But I was obsessive: in at six, spent all my evenings reading cook books. At the weekends, I moonlighted at 192 [in Notting Hill, alongside his Cambridge contemporary, Alastair Little]. It was a monkish existence, really.' When he was first approached about Kensington Place, he ummed and aahed for ages, but he had his vision - for a new kind of brasserie - and when he was finally offered his own share, he jumped. It's a decision that, through all the many ups and downs, he has never regretted.

It goes without saying that Le Café Anglais will be another success. OFM columnist Jan Moir raves about it on her website (areyoureadytoorder.co.uk), praising its 'soulful elan' and calling it 'the best restaurant to open in London for a very long time'. If this were anyone else we were talking about, the location might be problem but, as Simon Hopkinson says: 'He's so good that he could be in a dark basement in Ealing and people would still go.' When I get home after our talk - I take my prototype menu out of my bag, and start choosing the first of at least half a dozen imaginary orders. I'm writing this a few weeks later, and I pretty much know the thing by heart now, which means that I also know what my first real order - assuming the menu hasn't changed too much - is going to be (if only I could get a sodding table: I've tried three times now but it seems to be fully booked pretty much every night). I will, of course, have the pike boudin with lobster sauce (I, for one, do like pike; it's also the only fish to be celebrated in a song by the Stone Roses), followed by glazed pheasant with escarole, chilli and walnut sauce. If I'm setting myself up for disappointment, I can't help it. I really am very excited about Le Café Anglais - and I believe that, underneath it all, its chef is probably quite excited, too.

Le Café Anglais, 8 Porchester Gardens, London W2, 020 7221 1415, lecafeanglais.co.uk