Never eat anything bigger than your head, and never eat Italian food on a first date. Two valuable pieces of life advice that I'm wilfully discarding, except that technically this is not a date, it's an interview, obviously. But when you're at a table for two with a handsome Italian in a sleek suit watching attentively as you try to hold a conversation while grappling with a fresh molten pizza the size of a London borough, it's difficult not to feel acutely self-conscious about whether there are bits of rocket stuck in your teeth.

Roberto Di Matteo, the Chelsea midfielder with 26 caps for Italy, who made history first with his £4.9 million transfer from Lazio in 1996, and then with the fastest ever FA Cup Final goal (in 1997 after 42 seconds), is not eating but scrutinising every forkful I pick up, which makes it even trickier.

'It's all right, the pizza?' he asks anxiously, leaning forward. So I nod vigorously, hoping to convey that it's very much all right, the pizza, in fact it's excellent, and if I'm not eating as heartily as he might have hoped, it's only because I'm concerned to maintain a little poise by not dropping hot mozzarella down my front.

Inside Baraonda, Di Matteo's latest restaurant venture which opened last October in Heddon Street, W1, candles flicker against the orange-washed arching walls and the air is thick with the smells of basil and garlic. You might almost imagine yourself in Tuscany, if London were not in the grip of a Narnian eternal winter, with sheets of would-be snow sluicing down the glass. 'When the weather's better we'll have tables outside,' Di Matteo says, gesturing carelessly to the pedestrianised area through the window. 'I think it will look quite Mediterranean.' We glance up at the belligerent sky and he smiles. 'Maybe. With a bit of imagination.'

Baraonda ('It means "chaos". We liked that idea') is the second restaurant Di Matteo has opened with his business partner Roberto Caravona, after the success of Friends in Chelsea's Hollywood Road, his professional manor. 'Basically it was going well so we thought we would try another one in the West End. When we first saw this place, it was just the four walls. We had to do everything. All the ideas for the decor, we thought of them.'

With Beckham leading by example, it's not unusual these days to find Premier League footballers mingling with pop personalities and barely pubescent MTV presenters in many of London's celebrity restaurants, but Di Matteo is in a different category. A love of food and the carefully tuned ambience of a good restaurant have been an integral part of his life since childhood, and it's not just about being seen in the right company; you can't imagine any English player manifesting a similar level of excitement over the minutiae of interior design. 'You see these tiles?' - he taps the thick brick-red slabs with the tip of his immaculately glossy shoes as he leads me towards the stairs - 'these came from a farm that was being demolished in Tuscany. We bought the whole lot and had them brought over. And these little dishes, we put the olives in these. They are hand painted from Sicily. All the ingredients we import from Italy - apart from the fresh produce, of course. We really want it to be authentic.'

Even the chef, Fabio Rossi, is imported - 'We found him in Rome,' Di Matteo says over his shoulder, descending towards the basement bar and the kitchen. 'He used to work for a very famous restaurant there, La Pergola, and we approached him. He was very happy to come over for this adventure.' Rossi is small and slight and has a Tolkienesque air about him, scuttling round his underground kitchen, stirring and smelting and producing several dozen miraculous-looking things at once while chatting on all four cylinders in Italian. 'What is this?' Di Matteo glances into a saucepan and turns to me. 'Oh - sformato di melanzane con sfogliatina ai funghi porcini - you have to try one of these, it's fantastic.' I have no idea what's just been ordered and I'm really not hungry, but I don't want to be ungrateful so I smile witlessly and say 'Gracias', which doesn't fool anybody.

'Food was always such an important part of my family life when I was growing up,' he says thoughtfully, back upstairs in the main restaurant with a refilled glass of the ripe house red - me, not him. 'I won't have a drink now, I have to be careful.' He grins, and leans back, spreading his arms out over the back of the bench against the window. 'I mean, you can drink in moderation, the same with eating, but I am in here maybe three or four times a week and I have to watch my figure. Where was I?'

Family. 'Oh, yes. Well, I grew up in Switzerland where my parents were immigrant workers, but my whole family are very good cooks - my father also. So I always saw my parents enjoying to cook and prepare the food. In Italy it's such a big social function too, you know - when you meet all your friends you invite them for dinner or you go out to dinner. We use food very much for socialising and that is what I wanted in starting a restaurant.'

So was this always a dream that existed alongside the hopes of footballing glory?

'It was something I always wanted to do, to own a restaurant, because I love food. But particularly when I first moved to London, because I was on my own - I was single, away from my family, so it seemed very important, to have a place where you could go to meet friends and eat.'

Hence the name of the first restaurant, I suppose. 'Yes. I got in touch with Roberto when I first arrived because we had a mutual friend in Rome and he had been in London for a few years, so this guy suggested he should show me around. So we became good friends. And I'll tell you how the idea came up - it was the summer of '97 and we were sitting in Hyde Park one day, we were both single and away from home, and we said "I wish we could just start a business, a little place where we can go and have dinner in the evenings" - because we used to eat out every night. We didn't think about making money, you know? As long as it didn't lose money. Because we're both doing it for a hobby - he runs an accommodation agency, so it was really just for fun. So we opened the one in Chelsea.'

Just then, my next course arrives; it turns out to be a stuffed aubergine pie with layers of wild mushroom. It smells great, but I'm still as stuffed as the aubergine; it's beginning to feel like visiting my relatives at Christmas, only with better food. 'You don't have to eat all of it,' he says, kindly. 'Just try some.'

The menu is largely modern European - sea bass, monkfish, calves' liver, salmon, lamb and various kinds of pasta - and the main restaurant boasts a corner with a wood-fired pizza oven where diners can watch Fabrizio, the pizza chef, demonstrating his art. 'We discuss our ideas for the food with the chef and then we decide together what will work on the menu,' Di Matteo says. 'We wanted to do something different with this restaurant - Friends is more traditional Italian, and we wanted this to be something more modern. I usually have the calves' liver when I come here, it's very good. Or the seafood risotto. Or pizza - my favourite is this one, we call it Baraonda - it's rocket salad, cherry tomatoes, Parma ham and buffalo mozzarella.'

He also chose several of the wines on the list. 'This one, Montepulciano D'Abruzzo D.O.C - my parents are from Abruzzo. Or this is a very good one, or thisÉ' he points them out. Perhaps the most striking aspect of Baraonda is that it's affordable - he hasn't remotely set out to create a showground for celebrities and hangers on, though when he's not at his own restaurants he visits the usual places - Nobu, San Lorenzo, Scalini. The average main course at Baraonda is around £10, the pizzas nearer £7, and the most expensive wine on the list is a mere £55(we don't try this one, sadly). 'It's mainly a younger crowd who come in the evenings,' he explains. 'Well, older people too, but because it's not right on Regent Street we don't get all the tourists. I haven't done a lot of publicity, we wanted it to be more word of mouth.' And do the fans press against the door for a glimpse of him? 'Not so much here. They come to Friends more because it's near the ground, and they come and talk - I don't mind, as long as they're polite. I'm pretty easy-going. And some of the Arsenal players came here once in a group. And my team mates come a lot. A lot of people just come off the street and like the look because it's cosy. That's what we hoped for, anyway.'

No A-list celebs yet, then? He frowns, as if considering. 'Momento - Fabrizio!' The pizza chef lopes over, wiping his hands on his apron. There follows a lengthy dialogue, from which my crude grasp of Italian via Spanish allows me to extract the words 'television' and 'black'. Finally Di Matteo turns back triumphantly. 'Yes - he says that guy from Big Brother was in here the other day, the black guy.' Then he looks disappointed. 'I didn't see him, though.'

So does this Renaissance man ever take a turn in the kitchen himself? 'Here? Oh, no.' He laughs. 'But I do love to cook. When I have a dinner party I like to invite loads of people, then I would just do like a salad buffet, with some snacks and cold meat and lots of different salads. But if it's for maybe six or eight people, I cook pasta. I like to do tagliatelle with salmon and vodka. Not too much vodka, just a little bit. It's a creamy sauce - I learnt it from my parents. They live in Italy now so when I go to visit they love to cook for me. Maybe my favourite traditional Italian dish is one they always cooked for me when I was a kid - Bocatini alla Matriciana. It's a Roman dish - bocatini is a kind of pasta like spaghetti only it's tubed and a bit wider. It's made with bacon and tomato, but it's important to add the right amount of chilli to spice it up to the right point. But you don't want to eat it if you're wearing a white shirt - it's very messy.'

Precisely why you should never eat Italian food on a first date, QED. Did the rugged, pint-swilling English players ever deride his culinary hobbies as unmanly when he first arrived? He produces an elaborate Latin shrug. 'I didn't really care what other people thought. I just did what I wanted to do, and if some people don't like it - that's life.'

We move on to the liqueurs; at least I do, hesitating momentarily over the grappa (we have a painful history) before opting for a safer limoncello. After a season marred by injury, is Di Matteo, at 30, looking towards his nascent restaurant empire as a future career? 'I don't know. Why not? I enjoy it very much. I think I have been lucky - London is a very good place to try a venture like this, because it's so multi-cultural. I certainly would not have tried something like this in Rome, people there are more closed-minded. And if I moved to another team in another country, I don't think I would try again. Maybe it could work in Spain, I don't know. But I'm very happy here for the moment.'

The restaurant is beginning to fill up; regulars pause to chat to him, and a group of young women arrive looking for a table. I hint that he must get a lot of groupies keen to sample his lamb fillets.

He pretends shock, then bashfully lowers his big, milk-chocolate eyes. 'Oh no! I'm not like that. I am not David Beckham,' he adds, with a knowing grin.