Scientific tests by a food watchdog are set to reveal that thousands of chicken products contain large amounts of water, plus the DNA of pork and beef.
Chicken produce is carefully monitored in the industry
The BBC has learned that the report from the Food Standards Agency is expected to reveal that thousands of tonnes of chicken used by caterers contain other undeclared elements.
The results will be examined by 20 local authorities across the UK.
They could prompt the launch of prosecutions within the industry.
A survey carried out 15 months ago for the food watchdog found that chicken in the catering industry could contain up to 26% less meat than declared on the packaging.
Portions were bulked up by extra water and other added ingredients.
To include such extras is not in itself illegal - but misleading or inaccurate labels are.
It also caused alarm, especially among those who do not eat beef or pork for religious reasons, to find out that chicken contained other animal proteins
The industry has been warned about deceiving labels, but in spite of this the agency says the "con" is continuing.
It says people are still led to believe portions are meatier than they are and more expensive than they should be.
Once the findings are published, local authorities will consider whether to press ahead with court action.