Cafes and restaurants across Britain have been selling chicken secretly injected with beef and pork waste, The Independent can reveal today.

In a hi-tech fraud run by firms in three EU states, food manufacturers are making bulking agents out of porcine and bovine gristle and bones that help inflate chicken breasts, so that they fetch a higher price.

The swindle was only detected by the Food Standards Agency (FSA) using new scientific techniques because the non-chicken material had been so highly processed it passed standard DNA tests.

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Thousands of restaurateurs and cafe owners are likely to have been conned into buying chicken containing the powder – which binds water into chicken breasts – while diners have been unwittingly consuming traces of other animals when eating out.

Britain's two million Muslims, Jews and Hindus are forbidden from eating either pork or beef. Muslims would ordinarily eat halal chicken and Jews kosher chicken sold through approved caterers and butchers.

The Hindu Forum of Britain described news of the adulteration, which will be confirmed publicly today, as "shocking and potentially very distressing". Its secretary general, Bharti Tailor, said: "Eating beef is expressly forbidden because cows are considered to be sacred as they are a representation of the bounty of the gods, even unknowingly. The fact that the protein powders injected into chickens served in restaurants and cafes contain even traces of beef or pork is horrific. And [the fact] that Hindus will have been eating beef contaminated chickens will be mentally agonising. Many will feel that they have broken their religious code of conduct."

The food regulator acknowledged the serious consequences of its findings. "Use of these proteins does not make chicken products unsafe, but it is important that people are given accurate information about their food," the FSA said.

The fraud has been taking place for at least the past two years, and still continues because of inaction by the authorities in three EU states, believed to be Germany, Netherlands and Spain.

The European Commission rebuffed British demands to ban beef and pork proteins from being added to chicken when first detected in the UK and Ireland in 2001 and 2003. Then, action was taken against a chicken company in the Netherlands and the authorities thought the problem had gone away.

When complaints began to surface again last year, the FSA launched a secret investigation to ascertain whether chicken – the most eaten meat in the UK – was being adulterated again. At first, scientists could not find any non-chicken protein because the meat had been "de-natured" (made unrecognisable). The Central Science Laboratory in York and York University developed special DNA market tests.

"It's like Olympic drug tests; they stay one step ahead of the testers," said a source close to the investigation.

Manufacturers in Germany and Spain are thought to be making the protein powders; Dutch firms inject them into chickens sold on to UK wholesalers supplying the catering trade.

Using a new DNA marker technique, the FSA tested five protein powders from three companies. All five were found to contain a non-poultry material identified as bovine collagen. Further tests found the presence of porcine material in two powders.

Tests picked up traces of beef in one of three chicken breasts.

In a report passed to The Independent, the FSA noted: "The study of a small number of injection powders used in chicken breast products has indicated the presence of undeclared, mammalian peptides, i.e., from a non-poultry source in the samples analysed. The analyses applied indicate the presence of bovine collagen in all the powders sampled and suggest the presence of porcine collagen in some of the powders."

It added: "Certification accompanying the powders claim they are produced only from a poultry source, however, the analytical results suggest this claim could not be substantiated."

Manufacturers can legally add water to chicken, for instance to improve succulence, but must declare water content of above 5 per cent. Fresh chicken meat sold by supermarkets or butchers cannot have any added ingredients. When the FSA alerted its continental counterparts, the factories involved were inspected but no legal action has been taken.

Some chicken products state on the label whether they contain hydrolised (chicken) proteins. The FSA advised consumers that they "may wish" to avoid such chicken. "If you are eating food from a restaurant or takeaway you should ask if the chicken served contains hydrolysed animal proteins," the FSA will say today. "Restaurants and catering establishments will have this information available to them."

Sue Davies, chief policy adviser at the consumer group Which?, said: "It's bad enough that when you think you're buying chicken what you're paying for is an awful lot of water and other animal proteins but if you want to avoid beef or pork for religious reasons it's going to be particularly shocking and annoying. There's a need for better enforcement action, or people will carry on doing this."

Religious views: Sacred products

Judaism

Jews are forbidden from eating pork as pigs are considered unclean animals. The Jewish dietary laws are the laws of kashrut (keeping kosher). Hence food in accord with Jewish law is termed kosher, food not in accord is treifah or treif.

Hinduism

Observant Hindus who eat meat almost always abstain from beef. The cow is sacred and beef has been forbidden in the Hindu religion and diet. Hindu society honours the cow and cow-slaughter is banned legally in almost Indian states. The largely pastoral Vedic people and subsequent generations relied heavily on it for dairy products and tilling the fields.

Islam

Muslims are prohibited from eating pork products. All meat must come from a herbivorous animal slaughtered and bled to death in the name of God by a Muslim, Jew or Christian, with the exception of game that one has hunted or fished for oneself. Food permissible for Muslims is known as halal food.

Protein problems: Contaminated chicken

2001

The Food Standards Agency finds chicken with as little as 54 per cent meat and undeclared protein. The FSA urges the Netherlands and Belgium to tackle exporters.

2003

The FSA and the Food Safety Agency of Ireland find beef and pork in Dutch chicken. The FSAI warns that the EU and the Dutch are failing to police labelling rules. The European Commission rejects a call to ban beef and pork proteins, saying the matter is "primarily an infringement of food labelling legislation".

2004-2007

No new surveys on chicken are published. Many believe the problem has gone away.

2008

FSA investigates new allegations, but pork and beef cannot be detected by conventional DNA tests as it has been "de-natured" (rendered unidentifiable from its origins).

2009

Test results are obtained by The Independent.