Several brands of wholesale chicken portions sold into the catering market have been condemned by a Food Standards Agency (FSA) report for containing undeclared water and animal protein.
In a scam which the FSA has described as "completely unacceptable", 11 brands labelled as "halal" - meaning that the animals should have been slaughtered according to Muslim law - tested positive for pork proteins, strictly forbidden for Muslims.
Almost half of the 25 samples tested contained non-chicken DNA, including beef proteins.
Although not illegal, the practice of using water alone, or animal protein combined with water (hydrolised protein), to bulk up the weight of the chicken must be recorded on the label in order to comply with food labelling regulations.
However, in this survey, 18 of the 25 samples tested were found to have misused the terms "chicken breast" or "fillet", which can be applied only if the product has no added ingredients.
Samples tested had been supplied by one of 10 EU plants: one in the UK, two in Belgium and seven in the Netherlands.
An FSA spokesman said that, since all European chicken was subject to the same law, they were treating this as a "deliberate con".
Responsibility for cracking down on the practice among wholesalers and meat processors now lies at local level, with trading standards officers.
However, a trading standards spokesman for the London Borough of Newham warned caterers that, under the law, they could also be liable for not demonstrating due diligence when purchasing and serving food products.
Among the brands accused by the FSA of mislabelling are: T Lelie, TL, De Kippenhof, Rohim, Fraas, Marky, Duke, MR Brand root dz, Olympia, Josef Hassan and Aryt.
By Dan Bignold