Gordon Ramsay is not someone who does things by halves. Unsurprisingly, the crowning glory of his new house is the half-million pound kitchen, a room designed and built as an extension, with underfloor heating and whose centrepiece is a £67,000 Rorgue cooker. Weighing two-and-a-half tonnes, it was hoisted over the house by crane and then the builder put the roof on. It's a beast of a thing that leaves an Aga in the shade. 'It's about the same size as Gordon's car,' says his wife, Tana, 'and he loves it probably more.'

The Ramsays are justifiably proud of their new south London house which they bought in 2002. They'd been looking for some time, driven mainly by the need for more space for their four small children. 'We saw the board, rang the agent and discovered it was up for auction by sealed bids in two days' time, so we had to guess a price and submit it.'

The Ramsays carried the day, and the builders moved in to transform four flats with an exterior concrete staircase back into the eight-bedroomed family home it must have originally been in Victorian times. There were some pleasant surprises: Gordon and Tana hadn't realised that the gate at the end of the sizeable garden led into an enclosed five-acre park for the sole use of the 15 surrounding houses, with a tennis court, trees to climb and plenty of space for the boisterous junior Ramsays, who are applying steady pressure for a chocolate labrador puppy. At the moment the sole family pet is a rabbit called Daisy that Gordon regularly threatens to cook.

Despite its formidable size, this is very much a family home. The top floor is used for the children's bedrooms: the three girls - Megan, five-and-a-half, Holly, four, and Matilda, two, have interconnecting rooms; Holly's twin, Jack, is across the landing in his own blue room with a Sheriff's tent and framed, signed Glasgow Rangers shirt (Gordon played for their junior team). The first floor is Tana and Gordon's with their bedroom (neat, predominantly cream, nifty TV at the foot of the bed that rises out of a chest), his office (pretty chaotic) and their enviable bathroom with log fire, flatscreen TV and great view of the park from the huge free-standing bath. The basement is also a children's area, with a big playroom that leads on to the garden, and utility room for the mountains of washing, which includes Gordon's chef whites - two jackets a day soaked in Napisan.

The basement also accommodates Tana's kitchen where she cooks for the children. She mainly shops online at Waitrose and Sainsbury's, and buys her meat from Randall's on Wandsworth Bridge Road. She cooks on a Smeg Opera, a lot more modest than the one upstairs, and does plain, organic fresh food for the kids - home-made burgers and fish fingers, pasta and shepherd's pie, about which Gordon teases her mercilessly. 'When I was single I never cared much about cooking,' says Tana, 29, who met Gordon when she was going out with his friend. Pretty and svelte ('I jog, but apart from that I keep fit running round after the children'), Tana is tanned from two weeks at the St Geran, in Mauritius, with her husband. They do this every January, leaving the children with the nanny, Jana, and one of the grannies. 'It's a boyfriend/girlfriend holiday,' says Tana, 'and it's really important for us.'

Given Gordon's schedule, it must be. He leaves home at 7.30am and rarely gets home before 1am. After a gang of three men tried to get into the house last summer when Tana was there alone with the children there is now CCTV as well as the internal alarm.

Weekends are valuable family time when they rarely plan anything - mainly because weekdays are run to a pretty strict timetable, particularly now Tana has gone back to work three days a week. She runs her own shop, The Red Fort, in Knightsbridge next to Gordon's Boxwood Café, selling wonderful Indian furniture, jewellery, textiles and great household things all sourced by Tana in Rajasthan. 'I talked it through with Gordon and he's fine with me going back to work, and I always collect the big ones from school and take them home.'

Tana's former job as a primary school teacher is very useful. 'They'd all have detention by now,' she remarks at one point over the howling as Jack falls on his head and Matilda shuts her hand in a door. At weekends they'll often call in a takeaway from the local Indian, Bombay Bicycle, or go to Pizza Express, where nobody knows Gordon's a three-starred Michelin chef. The one inflexible food rule for the children is: 'Don't say no until you've tried it.'

'I don't want to bombard them with elaborate food,' he says. 'They're too young. Tana's careful not to give them too much salt or sugar, and we'll do things like make a fresh tomato purée instead of ketchup.' This is on the menu today, to go with the home-made cod fingers and thick chips. The children dutifully taste it and all then politely request 'the other ketchup'.

'I use the odd threat with them,' says Gordon. 'I tell Jack if he doesn't eat spinach his widger won't grow. When I was growing up there wasn't much money, so it was a case of "clean your plate". I'm very aware of our good fortune here.'

Mrs Ramsay's fish fingers, chips and tomato relish

Find any good quality white fish and cut into goujons. Roll first in seasoned flour, then in egg and finally in breadcrumbs. Shape into fingers by rolling between the palms of your hands. Put in fridge till needed.

Use large Charlotte potatoes, wash well and cut into wedges. Season well with rock salt and coat with plenty of olive oil.

Throw in some sprigs of rosemary, place on a baking tray and then into a hot oven at 210 C. Stir frequently and remove when crisp and golden.

Tomato relish

2 punnets of cherry tomatoes, halved

1 red onion, finely chopped

1 tbs icing sugar

1 tbs balsamic vinegar

Sauté the onions in olive oil until softened. Add icing sugar and lightly caramelise. Add tomatoes and stew for about 5 minutes until soft but not mushy. Deglaze with vinegar, season and serve.

Megan Ramsay's chocolate chip cookies

250g porridge oats

125g dark chocolate drops

50g blanched almonds, chopped

75g roasted hazelnuts, chopped

1.5 tsp salt

125g soft brown sugar

1 large vanilla pod, split and seed scraped out

2 large free range eggs

125g butter, softened

Mix the dry ingredients, from the oats to the sugar, in a big bowl. Beat the vanilla seeds into the egg and mix into the dry goods, followed by the butter, working with a wooden spoon until a chunky dough forms. Scoop onto a large sheet of clingfilm, shape into long sausage about 5cm thick. Wrap and chill until solid (overnight if possible). Heat oven to 200 C, gas mark 6. Cut the slices about cm thick and space them on a non-stick baking sheet. Bake for 14-15 minutes.

· The Red Fort, 41-45 Knightsbridge, London SW1 (020 7838 9777)