More than 50 birds from Taiwan died last month in a British quarantine centre where they are believed to have introduced a lethal strain of the bird flu virus, the government said today.
However officials said tissues samples from the finch-like mesias were pooled so it was impossible to say how many of the 53 dead birds had the lethal H5N1 strain of avian flu.
The government also said because tissue from a parrot imported from South America that died at the centre was pooled with a mesia sample it could not say with certainty which bird had introduced the virus.
Britain said last month a parrot held in quarantine east of London had been found to have had the H5N1 virus and that another bird held there, a mesia may have also caught it.
Standard procedure involves pooling of sample tissues from the dead birds, officials said.
A spokesman at the Department of the Environment, Food and Rural Affairs said all the cases were contained within the quarantine area and that there had been no threat to Britain's bird flu-free status.