Eleven days after a swan with the bird flu virus was found in a seaside village, scientists still do not know what species it is, they said last night. Officials suggested last week that it was a resident mute swan, but DNA tests are being carried out to provide a positive identification. As a native bird it could only have caught flu from another bird flying to Britain, possibly a summer migrant arriving in the past few weeks. In that situation, the H5N1 virus that has killed more than 100 people worldwide could have been spreading through Britain’s bird populations for some time. If the tests reveal that the carcass is that of a migratory species, such as a whooper swan, Britain could still escape a serious outbreak.

An infected migrant could have died while flying across the North Sea, before being washed ashore. Mark Avery, the director of conservation for the RSPB, said it was "pathetic" that scientists had not yet identified the headless carcass, recovered from the harbour in Cellardyke, Fife, on March 30. He added: "Whenever you have a case like this you need to know the species so you can better understand how the virus got here, how it has been transmitted and what the consequences are. It ought to be standard practice whenever there is a bird brought in with a suspicion of bird flu." A Defra spokesman said it was difficult to identify the headless bird, but it appeared to have the characteristics of a mute swan. She added that DNA tests at the Central Science Laboratory in York could be completed today.