Catastrophic lapses in anti-BSE controls have resulted in meat from at least three cows being eaten by unsuspecting consumers.
The animals were born to cows diagnosed with the disease and were meant to be kept under strict movement restrictions by farmers until they could be examined and destroyed by government officials.
But one each in November, December and last month went to abattoirs in Wales and were slaughtered for food. Only in the last case has any meat been recovered.
The Department of the Environment last night refused to give many details of where the lapses occurred, saying these might prejudice its investigations and any legal action. Such breaches could attract fines of £5,000 and/or three months imprisonment. The department blamed a backlog in animals awaiting slaughter because of pressures caused by foot and mouth last year.
Groups representing the families of victims of variant CJD, the human form of BSE, last night expressed deep concern. Frances Hall, of the Human BSE Foundation, said: "This is mind boggling. This is too dangerous to take chances with and there is no excuse. Foot and mouth was not dangerous to humans, BSE certainly is."
The Consumers' Association said: "Although these measures are introduced on a precautionary basis, it essential they are properly enforced."
The latests errors coincide with a worrying rise in BSE cases among animals born after feed bans meant to throttle the disease. The food standards agency said the likelihood of the three animals also having BSE was low but also expressed concern. Officials are privately furious at the department, which admitted the two later cases yesterday, a month after the first came to light.
Sir John Krebs, the agency's chairman, has not had a reply to a letter he wrote to ministers then urging them to tackle the backlog, and was last night writing once more. The agency said tissues most likely to carry BSE are removed from animals slaughtered for food as a matter of course.
A spokeswoman said it would not try to trace the meat. "There is no significant public health risk to warrant it." Animal health minister Elliot Morley said: "We are urgently checking to see whether there are any more cases and tightening procedures to reduce the risk of this happening in future."
The first case is understood to have been discovered when vets went to destroy the animal. The other two came to light as a result of checks after that mistake.