The Government was criticised today for "confusion" surrounding its handling of the bird flu outbreak at a quarantine centre in Essex.
More than 50 birds died at the facility where H5N1 was found, a report published by Defra says.
A consignment of Taiwanese mesia birds was the most likely source of the virus, which it was first thought may have come from a South American parrot.
Positive H5N1 results came from a pool of tissue samples taken from the blue headed parrot from Surinam and a mesia from Taiwan.
Because the sample was pooled, it was not possible to say from which bird the virus came, the National Emergency Epidemiology Group report published by Defra says.
But "on the balance of probabilities", the infection was introduced to the quarantine centre by the consignment of mesias from Taiwan, the report said.
The shadow environment minister Oliver Letwin said: "This is yet another worrying indication that confusion reigns.
"It is now clear that the original reports of what went on at Pegasus Birds were misleading yet we still have no answers on the crucial questions: which birds, if any, were released which could have been infected and what has happened to these since? Until these questions are answered, no one can be confident that Defra has the situation under control."
The infection was transmitted between mesias, but from the available evidence it did not appear to have been passed on to other species held at the facility, the report says.
Some 53 of the 101 Taiwanese birds died, though the report was unable to say how many were killed by the flu. The virus detected is most closely associated with Chinese ducks.Reuse content