Food safety officials were right not to recall beef which may have been contaminated with mad cow disease, the government has said.
BSE cases peaked in 1992 and have fallen due to safety measures
Rural Affairs Minister Alun Michael said the meat was considered to be at "very low risk" of carrying BSE.
In August 2004, 11 carcasses in a Scottish abattoir were found to contain thymus tissue, which must be removed under BSE safety guidelines.
A carcass from the same abattoir, which may have contained thymus, was sold on.
Mr Michael said: "The matter, as far as we can see, was dealt with entirely properly.
"No recall was instituted by the Food Standards Agency (FSA) because the meat was already likely to have been eaten, difficult to identify and, more importantly, likely to be of very low risk.
"BSE itself is in steep decline; GB cases actually peaked at over 36,000 in 1992 and had fallen last year to 309," he told MPs in the House of Commons.
The Food Standards Agency said it did not alert the public because of the "very low" risk of BSE and because the meat would already have been eaten.
It stressed that it had formally reported the incident and made follow-up checks as soon as it became known last September.
All cattle which go into the food chain must have specified risk material removed to protect the public from contracting the human form of mad cow disease.
This includes the spinal chord, head and thymus.
An investigation by the Food Standards Agency found that a vet and the Meat Hygiene Service had failed to spot risk material on the 11 carcasses.
A carcass which might have been contaminated was bought by a butcher and sold on to the public.
Following the incident, which was reported on the agency's website and at two public meetings in September of last year, 71 other abattoirs were checked and tighter inspections were put in place.
No other breaches in guidelines were discovered.
The Food Standards Agency told BBC Radio 4's Farming Today programme the meat was not recalled because it was "very likely" it had already been eaten.
"The risk was very low - it was not certain that the thymus was still in the carcass and this would have been an under-30 month animal," it said.
"There have been no cases of BSE in under-30 month animals since 1996."
BSE was in steep decline with 309 cases last year compared with a peak of more than 36,000 in 1992, it added.
BSE experts in France said in January that safety precautions were sufficient to protect humans against mad cow disease.
Banning brain, spinal tissue and older cattle from the food chain had worked, a French team told the Lancet.
By studying monkeys, they estimated how much infected tissue a human would have to eat to be at risk and said it would be more than anyone could consume.
However, UK experts said the exact quantity remained unknown and recommended continued surveillance.