Levels of potentially dangerous drug residues in chickens destined for the dinner table may well be higher than suggested by government figures, according to a new report by organic farming group the Soil Association.

The Ministry of Agriculture (Maff) maintained that there has been no attempt to mislead the public, and stressed that of the samples of chicken meat it tested last year, 99.5% were free of any drug residue.

In a statement, Maff said: "It is important to stress there has been no attempt to mislead or misrepresent any figures. All test results are fully reported every year and have been since 1995 […] The residues mentioned in the Soil Association report were all found at levels well below World Health Organisation safety limits."

On of the report's authors, Richard Young, has challenged the government's statistics however, commenting: "Despite repeated assertions by regulators that nearly all poultry products are free from detectable residues, figures show clearly that about 20% of chicken meat and 10% of the eggs tested contain residues of drugs deemed too dangerous for use in human medicine."

Drugs such as antibiotics are routinely employed by poultry farmers to treat sick birds, prevent disease or promote growth. According to the report, however, several drugs used to treat parasites raised serious potential health problems for human consumers. Nicarbazin, which was found in 18% of chicken livers tested and in about 2% of eggs, is believed to cause birth defects and hormonal problems in animals. Lasalocid meanwhile is not even licensed for laying hens, but it was found in one in every dozen eggs and about 12% of chicken muscle. It is believed to damage the heart. Dimetridazole, which is suspected of being able to induce birth defects and cancer, is licensed for use in turkeys and pheasants, but had been found in one in 200 chicken eggs in 1999.

British consumers eat over 750m chickens every year, low prices and red meat food scares meaning that chicken accounts for nearly 40% of all the meat sold. An independent Veterinary Residue Committee has been established by the government to investigate the issue further.