In the last half-century, curry has become more traditionally English than English breakfast. Robin Cook believes that chicken tikka masala is now our national dish; there is a Koh-I-Noor or a Taj Mahal on just about every High Street in the country. It was entirely fitting that David Beckham celebrated scoring the goal that qualified England for the World Cup at Manchester's Shimla Pinks, with what we are told is 'his favourite' chicken korma. Madonna, more and more the Anglophile, has apparently taken to ordering the 'taxi curry takeout' from the Noor Jahan restaurant near her London home in Westbourne Grove.

The most extraordinary thing about the Balti Houses and Rajput Tandooris up and down the country is that each and every one of them has the same menu. You can find more or less identical lamb pasandas and chicken vindaloos in Bradford and Brick Lane, Alderley Edge and Virginia Water. Indian food is a £3.2 billion industry in Britain, accounting for two-thirds of all eating out. But until recently, all the available dishes were based on a couple of sauces, alternatively spiced up with chillies or cooled down with yoghurt or cream. The resulting concoctions have only a tangential relationship with food as eaten in India. The balti, for example, was invented in Britain, probably in Birmingham. Various derivations of the word have been offered - that it's a region between India and Pakistan, and, no less mischievously, that it's a dialect word for a bucket. But no one actually knows what it means.

The homogeneity of Indian restaurant food is even more surprising when you consider that India is around the size of Europe and at least as topographically varied: thousands of miles of coastline, vast arid plains, marshy lowlands and extremely high mountains. Diet is also determined by religion and caste. More than half the population is vegetarian, the Parsees are influenced by the Persians, the southern Muslims by the Malaysians; some southern Christians by Irish missionaries; and the Jains don't eat anything that grows underground. So talking about Indian food is scarcely more informative than talking about European food when you actually mean Italian or Portuguese.

We all know why this has happened. More than 90 per cent of Indian restaurants in Britain are owned and run by Bangladeshis. Initially, it was next to impossible for them to reproduce their home cooking, which involves a lot of seafood and vegetables that were difficult to source here then at sensible prices, certainly in a sufficiently fresh state. And, as restaurateur Iqbal Wahhab, himself a Bangladeshi, points out, 'Bangladesh as a brand is associated with floods and cyclones, whereas India is associated with romance, the Raj, the Taj Mahal, mystique'.

Most of the would-be restaurateurs hadn't been cooks at home, so it almost didn't matter what food they made. (There is a theory that if the garment trade had remained more successful, there would have been no Indian restaurant explosion.) And when a successful formula was found, it spread like wildfire.

The hybrid Bangladeshi-Indian curry house is a much-loved institution, but its cooking is scarcely inventive. And though the food may be irresistible in its way, especially on a Saturday night after a few pints, it's not exactly of the highest quality. As Pat Chapman, the founder of the The Curry Club (an organisation that promotes Indian food), explains, the classic curry gravy will include taste enhancers such as 'factory-bottled curry paste, garam masala, asafoetida, fenugreek seeds and even some chemicals. Monosodium glutamate enhances taste and thickens sauces. The restaurateur achieves his bright oranges, reds, yellows and brown colours using powdered food colouring and then there's tinned tomatoes and tomato puree and ketchup, and sweeteners such as sugar or even pureed mango chutney.' Still fancy that chicken Madras?

In the last few years, something very different has been happening to Indian food. Curry has got posh. Most strikingly, two London restaurants, Tamarind and Zaika, have each been awarded a Michelin star, and there are several other contenders - The Cinnamon Club, the Red Fort - snapping at their heels. The British consumer, long familiar with biryanis and bhunas and increasingly sophisticated about spicy flavours, is ready to try something new. Waitrose has been selling a Goan dish called Xacutti for about three years. You might have found this in one of the very few restaurants specialising in Goan food (such as Cyrus Todiwala's Cafe Spice Namaste at Aldgate East and Battersea) but never in your local curry house.

Britain's growing discernment about Indian food has coincided with a deepening appreciation of the country. India has ceased, in the British mind, to be about the Raj and poverty-stricken villages, and become the home of computer programmers, call centres serving British companies and such striking films as Lagaan and Monsoon Wedding. Bollywood has also become cool, in a semi-ironic fashion, with Andrew Lloyd Webber's Bombay Dreams about to provoke even more interest. Meanwhile, the Asian British experience is a hot subject for books and films (Bend It Like Beckham, Anita and Me, Goodness Gracious Me, The Kumars at Number 42, Hari Kunzru's The Impressionist).

There's no longer a simple idea of India as a large hot country to which we gave a civil service, and which, in return, gave us curry. (A lot of 'us' are now Indian anyway.) Reflecting this heightened interest, Selfridges has this month turned over its London and Manchester stores to a Bollywood promotion. This week, the restaurant in the London store will be offering food from India's coastal regions: marinated, steamed and panfried claws to start perhaps, seasoned with crushed peppers, garlic, and lemon juice; coated with egg and tossed in coriander, mint and green chillies. And to follow maybe Magalorean chicken curry cooked in red chilli, peppercorn, cumin and coriander sauce, with onions, fenugreek and cumin, served with coconut rice and spinach. For the following two weeks, the food will be from the North-West Frontier, including, to start, fish tukra baskets - batter-fried cubes of salmon tossed with onions, tomatoes and peppers, served in a potato basket. To follow, there's dum ka kid gosht: lamb shanks cooked in gravy in a sealed pot; or maybe Bombay Brasserie lamb chops, cooked in the tandoor. (Taj Hotels are collaborating on the food, flying over 20 chefs. In the UK, Taj own the Bombay Brasserie, one of the first upmarket Indian restaurants here, and the Keralan restaurant Quilon.)

Meanwhile, in the food hall, around 50 different dishes are on offer, and there will be seven or eight stalls demonstrating street food: roasted corn flavoured with salt and red chilli powder with limes cut into it, or baida paratha - bread dipped with beaten egg, or puri, a kind of biscuit made with chickpea flour and topped with potatoes, yogurt, onions and coriander or perhaps with tamarind, or mint chutney.

The poshing of Indian food has mainly taken place in the capital, but it's inevitable that it will spread across the country. Italian food escaped its checked tablecloth and giant pepperpot origins first in London, but - not least through the efforts of Jamie Oliver, who is not Italian at all - Northern Italian/River Cafe-influenced food is now understood everywhere in Britain. Ironically enough, though, the British love affair with the curry house actually creates a lot of unwelcome baggage for the chefs and restaurateurs who are trying to increase understanding of Indian food. Iqbal Wahhab, owner of the Cinnamon Club in Westminster, complains that initial reviews all compared it to a curry house. 'We don't want to be seen as an Indian restaurant; we want to be seen as a London restaurant. I don't want people to say, "Shall we go to Indian restaurant one or two, or the Cinnamon Club?" but "Shall we go to Le Caprice or Nobu or the Cinnamon Club?" We're not quite there yet. But that's where we aspire to be.'

The Cinnamon Club is located in a former Westminster library, and not much about the coolly understated decor says 'Indian restaurant'. 'I wanted to leave the identity of the building intact,' Wahhab says. 'It's such a fantastic structure. I wanted it simple, elegant; no fancy tableware.' Everything, down to the £100-a-throw cinnamon-coloured calfskin menus, expresses comfort, discretion and affluence. Wahhab spent several years as a restaurant PR frustrated that even those of his clients who were serving very good food were insufficiently concerned about presentation and service - 'chutney splats on the menu, waiters filling the wrong glass first'. But the presence on the menu of dishes such as crab risotto and rump of beef with sauce bordelaise (Wahhab involved the French Michelin-starred chef, Eric Chavot) and a certain adventurousness on the part of Vivek Singh, the Cinnamon Club's hugely talented executive chef, seem to have left some people confused.

'Authenticity is a big bugbear for us, and for Indian cooking generally,' Wahhab complains. 'In France, no one's conditioned by Escoffier any more, so why are we so concerned that this is how a dish was made 200 years ago by some old git who's been passing the recipe down through one Lucknowi family? You hear this story everywhere: "My chef's got the only recipe because his grandad gave it to him, and his grandad gave it to him, and his father cooked for the king of so-and-so."

'People say to me, "Is your food authentic?" And my response is, "Do you mean good?" What does authenticity mean anyway? Flies in your food, cholera, dysentery? It could mean any of those.' The truth is that all the classy Indian chefs emphasise their authenticity when it suits them, and ignore it when it doesn't. By definition, great chefs are driven to experiment and create. So when Rajesh Suri, the general manager of Tamarind, says: 'I believe very strongly that you can present Indian food any way you want to, but you can't lose the identity of the cuisine - a rogan josh has to be a rogan josh', and adds severely: 'Certain people are trying to confuse', he is only telling half the story. As he adds later: 'There aren't too many traditional dishes, and while we do remain faithful to those, we have to create our own as well. So we have a selection of traditional and chef's own creations.'

Back at the Cinnamon Club, they do serve a rogan josh, for which they import a spice called the rattan jyot, the bark of a tree that imparts the dark red colour to the lamb curry. 'Nobody knows about it or has seen it in this country,' Vivek Singh says. (Here, it's usually done with tomatoes and paprika.) In common with other top-class Indian restaurants, the Cinnamon Club imports many spices directly. 'A Rajasthani dish with coriander grown in Kenya somehow doesn't taste the same,' Vivek says. 'We might serve a Rajasthani lamb curry with lemon rice from the south of India, but the Rajasthani lamb curry itself must be authentic.'

Red chillies are brought in from Rajasthan; pepper, cinnamon and cardamom from Kerala; mustard from Bengal; rattan jyot from Kashmir; and rock moss from Hyderabad. This last ingredient, which looks exactly as it sounds, doesn't taste of anything, but brings out the favour of biryanis. 'A real biryani requires a high level of skill,' Vivek explains, 'because the marinated meat is covered with rice that is already two-thirds cooked. Then it is sealed and steamed so that the raw meat cooks in the same time as the rice. It needs a large quantity to work.' The point about experimentation, I suspect, is that where it doesn't work it gets called fusion and where it does, it just gets eaten. The real question is whether the ingredients, in Vivek's words, 'are streamlined and disciplined, the flavours clean and clear and headed in a particular direction'. (People setting off for Nobu aren't worried that the food there isn't authentically Japanese, or even Peruvian Japanese, if they even knew what that was; they're too busy looking forward to the blackened cod. It seems likely that, as ever, great new dishes will survive, and those that are merely fashionable will fade away.)

Vineet Bhatia, the chef at Zaika, describes his food as 'modern evolved Indian cuisine' - probably a definition to which all serious Indian chefs would be happy to sign up. I doubt many people in India today are sitting down to scallops poached in coconut milk flavoured with mangoestein and with dry roasted and pureed spices, served with chilli mash, which I ate at Zaika recently. But the scallops were subtle and delicate - still recognisably scallopy but overlaid with intriguing, smoky spice, and the chilli mash was piquant and satisfying - the best flavoured mash I have ever had, in fact. Certainly, you'd have to search hard to find this dish in a restaurant in India, because there is virtually no independent restaurant tradition there. According to Namita Panjabi, owner of Chutney Mary, Masala Zone and Veeraswamy, 'until four or five years ago, five-star hotels were the only places you could go out to eat'. The hotels tended to serve versions of Mogul food, long seen on the subcontinent as haute cuisine because it used expensive ingredients and was the food of princes.

'The hotels made very commercial food - things like butter chicken. Nobody ever cooks a butter chicken at home. I would say 90 per cent of Indian hotels make three sauces. A red sauce, which is a tomato sauce, a white sauce which is a cashew sauce and a brown onion sauce. And then when the order comes they add the cooked meat or whatever.' In this country, as a result, all sorts of adjustments have quietly to be made for Western restaurant eating. 'Mealtimes in India have never been a time to sit down and have a conversation,' says Namita Panjabi. 'Eating is a much more sombre kind of thing, traditionally. You sit in the kitchen, on the floor, you eat quietly, for digestion, and then you get up and do whatever you want.'

Nor do Indians drink beer, let alone wine, with food. Upmarket Indian chefs all make a case for wine, not least, no doubt, for commercial reasons (although most accept that not all wines work). Rajesh Suri, general manager of Tamarind (the first Indian restaurant to have a sommelier, and which has an award-winning wine list priced from £14.60 to £600) says he sells a lot of pinot noir and sauvignon at lunch, and a tremendous amount of red Bordeaux in the evening, which starts at £40. Sriram Ayur, executive chef of the Keralan restaurant Quilon, says 'You need bolder wine with this food. White wine can get lost. I tend to think new world red wines work best.

'But beer with Indian food is a disaster. I love beer - I love Kingfisher - but I think it should never be drunk with this food. The gas is terrible because it reacts with all the spices, and the hops make it bitter, and you're already having a melange of sweet, spicy and sour, so why would you want this bitterness coming in? Everything is wrong with it.' Like so much else connected with curry (even the word itself, which does not occur in any Indian language, though there's a cooking pot called a korai and a spice called a curry leaf) the origins of lager-drinking with Indian food are mysterious. Namita Panjabi has been told that in the early days of Veeraswamy in London's West End, which was founded in 1927, the King of Denmark came whenever he was in the country. Frustrated at not being able to drink Carlsberg - which wasn't then available here - he shipped over a barrel, so that when he came to eat it would be available for him. And so began a great, or not so great, tradition.

Apocryphal, possibly, but a nice story. Veeraswamy wasn't the very first Indian restaurant in Britain; in 1809, Sake Deen Mahomed, an Indian who had married an Irishwoman, opened Deen Mahomed's Hindustani Coffee House in London. (It doesn't seem to have caught on: by the time he died in 1851 at the age of 101, the restaurant had closed and bankrupted him.) But it is certainly the oldest surviving, and in its early days, was distinctly upmarket. Edward VIII frequently dined there when he was Prince of Wales, and, the night after the boats from India berthed at the London docks, there was always an influx of maharajahs. Namita Panjabi and her husband bought Veeraswamy in 1997 with the aim of restoring the then unfashionable restaurant to its former glory. But where originally the decor had been exotic, all tiger skins and light fittings from maharajahs' palaces, the new owners opted for light, colour and freshness: plenty of blond wood, walls washed in purple, green and gold, menus glowing pink and orange. Panjabi's pitch, both at Chutney Mary and Veeraswamy, is that she serves 'gourmet food of the home' because, she argues, that is where the best and most interesting food is cooked.

'About 70 per cent of our dishes are pretty authentic, although we use much less oil than, say, my grandmother's generation and the meat and fish that are available here. And there's a much greater range than you would find in India. If you lived in Delhi, for instance, you wouldn't eat the food of Kerala unless you travelled there. And it seems to me that there is such a wealth of different cuisines in India that you don't need to mess about with individual dishes. The food of the Brahmins is very light and vegetarian, and then there are the Hindus who are not Brahmins, who will eat non-veg. Duck is eaten by the Christians. Muslims don't use vinegar as a souring agent, so I would never put it in a Muslim dish. There's no need.'

In common with other smart Indian restaurants, food at Veeraswamy arrives already plated. 'If you come out for the evening to converse and have a jolly time, you don't want to be stretching your arm across people,' Panjabi says. 'In a family you would eat out of bowls, but that would be because everything, the dahl, the vegetables, the bread, has been designed to complement the main dish. If you eat one prawn dish, one chicken and one lamb, it means that although the chef has taken hours to cook it, you're eating an amalgam of everything, like having coq au vin with boeuf bourginon.'

Desserts, like wine, present a trickier problem. There is no tradition of parcelling food up into courses in India. Starters and main courses can be separated out relatively easily for Western tastes, but Indian sweetmeats are too heavy and sugary to work at the end of a three-course meal. In India they are served for afternoon tea - as Iqbal Wahhab says, 'it's like eating scones after roast beef'. But the pressure to produce desserts that work for a British audience (clearly, it's much more lucrative to sell three courses than two) has produced some stunningly inventive combinations of fruits and spices. The Cinnamon Club has tandoori pineapple marinated in honey and saffron and grilled; or pastry stuffed with dates and cinnamon and served with cinnamon ice cream; Quilon has tropical fruits infused in honey, mint and lime, served with pepper ice cream. It seems likely that, as consumers become more sophisticated, the number of restaurants dedicated to regional cuisine will grow. The Rasa group, under the guidance of Das Sreedharan, has five Keralan restaurants in London. At Quilon, Sriram Aylur cooks Keralan food that is much lighter and more delicate than the curries of the north: fish in banana leaf; baby aubergine stuffed with coconut, red chillies, poppy seeds and coriander seed; delicate lacy-edged rice pancakes.

'In India you would never use just one spice; there's nothing like chicken with tarragon. A recipe might have 20 ingredients,' Sriram says. 'Indian food is so interesting partly because it is so scientific. In anybody's house, no matter in which part of India, every single ingredient that goes in has a reason to be there. Chefs make it sound like an art, so people believe it can't be done, but I think you have to translate it into chemistry. For example, you have to put the spices into hot oil, because the oils in the spices are oil-solvent, and hot oil tends to penetrate and release their flavour and aroma. You have to cook tomato on a low flame, because you want the acid to evaporate, and if you cook it too high, the water evaporates and leaves the acid behind.'

The other area that seems ripe for expansion is street food. There may not be many restaurants in India, but there is a legion of roadside stalls. 'Street food is food you stop your car for, even if you're 20 minutes late, even if you're on your way to dinner,' says Namita Panjabi. 'You can't control it, because you know this particular guy is famous for this one thing, so you have to make a detour. It's like an Indian tapas: hot, spicy, sour, sweet, all that complexity; and then the seductiveness of yoghurt.' Impressed by the success of the noodle-chain Wagamama, Panjabi wondered whether she could do something at similar prices with Indian food. The result was Masala Zone which opened in London's Marshall Street a year ago and now has 150 people in for lunch every day, eating little plates of street food. It has been a resounding success. One way and another, Indian food seems on the brink of a revolution in this country. Britain may even be at the cutting edge of Indian cooking. The curry house is not about to disappear. But the very existence of Michelin-starred Indian restaurants may signal the death knell of flock wall-paper, lager and an onion bahji. Thank goodness for that.

Sweet potato cake

Serves 4

Potato mix
250g potatoes (desiree), peeled and diced into 2 mm cubes
75g sweet potato, diced into 2 mm cubes
50g celery, peeled and diced into 2 mm cubes
25g carrots
3g cumin
3g fennel seeds
50ml vegetable oil
50g coriander, chopped finely
25 g corn flour

Filling
100g roasted sweet potato
30g pounded ginger
10g fennel seeds
5 g pounded green chilli
2g salt
10g sugar
clarified butter to shallow fry

Take boiled potatoes which are cooled down to room temperature, peel and grate. Peel and dice the carrot, raw sweet potato and celery in 2 mm dices. Heat oil, add cumin seeds and let them crackle, add fennel seeds and saute the diced vegetables quickly. Season with salt. Let the vegetables cool and mix with grated potatoes.

Add chopped green coriander, mix corn flour just to dry the mix, check for seasoning and keep the mix aside. Divide the mix into 4 parts and keep aside.

Roast one sweet potato with the skin in a slow oven (150-180c) until the potato is soft. Peel and discard the skin, mash the flesh with a fork. Pound the rest of the ingredients for the filling together in a mortar and pestle until a coarse paste.

Mix together the spice mix with the mashed roasted sweet potato. Take each ball of the potato mix and fill with the spicy sweet potato filling. Once all the mix is filled, shape them like cakes and shallow fry in vegetable oil or clarified butter until crisp and golden on both sides.

May be served with tamarind chutney and yoghurt or any chutney of your choice.

Executive chef Vivek Singh's recipe from his restaurant The Cinnamon Club, London

Currying favour

· Scots eat 50,000 curries a night.

· In April 2001 Robin Cook pronounced chicken tikka masala Britain's national dish.

· Britain's first curry house was the Hindustani Coffee House, opened in 1809 in London's Portman Square. It had a hookah for customers to smoke.

· Indian restaurants in Britain serve 2.5 million customers every week.

· By 2002, we will spend £3.5billion a year on curry.

· It was once thought that too much spicy food could lead to ulcers. There is now evidence that oils from chillies actually protect the stomach lining.

· Basmati rice is from specific geographical areas and is difficult to grow. DNA testing is used to make sure basmati coming into Britain is the real thing.

· Chicken tikka masala was created in Glasgow, but the identity of the inventor is an area of contention.

· If all the chicken tikka masala portions served in Britain in one year were piled up, they would form a tower 2,770 times taller than the Millennium Dome.

· Marks & Spencer sells 18 tonnes of chicken tikka masala a week.

Research by Caroline Palmer