A trading standards investigation has found dangerous levels of food colouring in chicken tikka masala. What are these chemicals, how do they harm us - and what other foods may contain them? Terry Kirby reports

Until now, the main criticism of the nation's favourite dish, scoffed in a million curry houses every Friday night, preferably with a couple of lagers, has been its distant relationship to real Indian food.

Until now, the main criticism of the nation's favourite dish, scoffed in a million curry houses every Friday night, preferably with a couple of lagers, has been its distant relationship to real Indian food.

But a far more serious accusation has now been levelled at chicken tikka masala: that, in the depths of its vivid pink-red sauce, it may be harbouring dangerous levels of chemicals that can cause hyperactivity, asthma, and even cancer.

Trading standards officers in Surrey have found that more than half of the Indian restaurants it examined were using "illegal and potentially dangerous" levels of food dye to give the dish its distinctive colour. And their findings have prompted a nationwide alert for their colleagues to ensure Indian restaurants everywhere adhere to legal limits on such additives. The warning once again highlights the use of colourings and other additives in the food that we buy in supermarkets and eat in restaurants

While there has long been concern about the use of monosodium glutamate, alleged to cause headaches, in some Chinese food, the Surrey research suggests that consumers of other ethnic foods should now be even more concerned as to how much of what they eat is tainted by chemicals.

Despite the growing emphasis on additive-free and organic food, the high street curry house and the pre-packed supermarket meal of Indian or other Asian foods remain as popular as ever. Takeaway and fast-food sales, much of which is "ethnic" food, rose by a third between 1997 and 2002. Sales of supermarket ready meals rose by 90 per cent in the same period.

The Surrey trading standards survey involved ordering chicken tikka masala from 102 restaurants and testing each dish for three specific chemicals commonly used as food dyes: tartrazine (E102), sunset yellow (E110) and ponceau 4R (E124). Only 44 were found to be within the legal limits.

While the colourings are only dangerous if consumed in large quantities, other countries have been sufficiently concerned to ban their use altogether. All three are claimed to be linked to hyperactivity in children.

Tartrazine, a dye made from coal tar, is banned in Norway, Finland and Austria because of concerns that it can cause blurred vision, purple skin patches and is hazardous for asthmatics and anyone allergic to aspirin. It is used in cakes, soft drinks and sauces, while some egg manufacturers feed it to their chickens to make their yolks extra yellow. Sunset yellow is also banned in Norway and Finland but elsewhere is used in juices, sweets and sauces. Scientists have linked it with chromosome damage and kidney tumours as well as abdominal pain, hives, nausea and vomiting. Ponceau 4R, which is illegal in the US and Norway, is believed to cause cancer in animals.

Phil Thomas from the Trading Standards Institute said there was no reason to believe the problem was confined to Surrey or to chicken tikka masala. "We are urging trading standards services across the UK to work with Indian restaurants in their area to ensure the amount of colorants used is within the legal limits," he said. "Consumers should have confidence in what they eat because you are not given information on what is in your food in a restaurant. It is a particular problem with curry sauces."

Ironically, British consumers only have themselves to blame if their chicken tikka masala is poisoning them. The dish was devised by Indian restaurants to satisfy British tastes by combining two other dishes, themselves only relatives of the cuisine of the northern part of the sub-continent. Chicken tikka is a kebab-style dish of pieces of chicken, marinated in yoghurt and spices and cooked in a tandoor - a clay oven. Masala is simply a name for a sauce containing tomatoes, herbs and spices. Legend has it that the first chef to make the link was in Glasgow in the 1950s when a diner demanded some "gravy" with his dry tandoori chicken: the chef added a can of tomato soup and some seasonings.

While in one sense, this was continuing a tradition of dishes combining British and Indian tastes - such as mulligatawny soup and kedgeree - a relatively minor culinary crime has been compounded by others who put it on pizzas, in sandwiches and used it as a flavour for crisps. Twenty-three million tikka masalas a year are now sold in restaurants in the UK.

And it is public taste which drives the market, Indian chefs pointed out yesterday. British men, who tend to like their curry hotter than the norm, confuse red with chilli-hot and expect their food to "glow in the dark". Traditional spices, such as turmeric and paprika, just do not do the job.

Jehangir Haque, proprietor of an Indian restaurant in Fetcham, Surrey, said that on one occasion he had been forced by a customer to bring out bottles of spices and colouring from his kitchen to explain why his pilau rice was yellow rather than multi-coloured. He said: "The perception is that if you don't put colouring in the customer will think that it isn't the original chicken tikka masala." Chad Rahman, of St Albans, the National Curry Chef of the Year 2002 and 2003, said: "There is no need to [add colouring] as regards the taste of the food. Colouring does not enhance the flavour of the food but a lot of people eat with their eyes."

While not many children eat curry, the fact that colourants make food more visually attractive underpins concern among about their use in sweets, soft drinks and foods that appeal to the young. Some surveys suggest that colourings are used in 78 per cent of

children's desserts, 42 per cent of milk shakes, 93 per cent of children's sweets and 23 per cent of children's cereals.

According to the Food Commission, which supports a ban on colouring, s uch popular sweets as Smarties and Jelly Tots contain both sunset yellow and ponceau 4R. Although scientific research has yet to make a definite link between hyperactivity in children and food additives, many parents feel the case is proved. Sally Bunday, of the Hyperactive Children's Support Group, said that out of 357 children on its books diagnosed with hyperactivity, 89 per cent were affected by artificial colours. "We believe they should be

just banned, as they are in other countries," said Ms Bunday. "Most studies tend to focus on the toxic, rather then behavioural or accumulative affects on children. But there is sufficient evidence to support our case that these are bad for children." This includes an officially funded study of 277 three-year-olds in the Isle of Wight, which showed that artificial colourings and sodium benzoate - a preservative used in fizzy drinks - in fruit juice affected the behaviour of hyperactive children.

The Food Standards Agency, which is responsible for warning the public about such matters, said yesterday that it could not comment in detail because it had been unable to obtain the research from Surrey County Council or access its website. It said the European Food Agency would be expected to examine the research as part of its review of all additives.

Ms Bunday also made the point that giving additive-loaded chicken tikka masala to young men with propensities for hyperactivity may suggest that late-night behaviour in curry houses is not simply due to lager consumption.


Sweet and sour prawns

Among the most infamous of flavour enhancers is monosodium glutamate (E621). It has long been linked to "Chinese restaurant syndrome," which can lead to faintness, numbness, sweating and headaches.

Sausages and mash

Sausage meat has been found to contain the additive cochineal (E120), a red pigment extracted from the crushed carcasses of a cactus-feeding insect. Also found in pork pies and maraschino cherries, the additive has been linked to a range of allergies.

Chicken vindaloo

Another chemical dye detected illegally in dishes in Indian restaurants is Sudan I, which can be found in chilli powder, relishes and chutneys. The dye was designed for shoe and floor polish and is banned from food in Europe because it is linked with cancer.