The Scottish Executive in Edinburgh said on Thursday a mute swan - found last week on a harbour slipway in Cellardyke, Fife - perished from the same H5N1 strain that has killed more than 100 people, mainly in Asia.
Charles Milne, Scotland's chief veterinary officer, said The Veterinary Laboratories Agency was carrying out tests for possible bird flu in 12 swans and two other species from Scotland.
Two swans found dead in the Scottish city of Glasgow, 645km north of London, are among the 14 being tested for H5N1.
Milne said there were no indications so far that any of these results were positive, but added: "We will have to wait until the laboratory tests are completed."
Debby Reynolds, Britain's chief veterinary officer, said the discovery of one bird flu case followed tests on thousands of wild birds this year alone, but she refused to speculate on whether this was an isolated incident.
No serious risks
Health officials said the case poses no serious risks to public health but the government began restricting poultry movement and implementing a 2,500-square-kilometre "wild bird risk area" around the site where the infected swan was found.
Poultry farmers within the risk area will be required to bring their flocks indoors, with around 260,000 birds expected to be moved.
Tests are being carried out on
12 more wild swans
Peter Kendall, the president of National Farmers' Union, urged the public to stay calm and said poultry was safe to eat.
The World Health Organisation said on Thursday that at least 109 people have died from bird flu since a wave of outbreaks of the H5N1 strain swept through Asian poultry populations in late 2003.
Virtually all the individuals were exposed to the disease following direct contact with infected birds.
But health experts fear the H5N1 virus eventually will mutate into a form that spreads easily among people, potentially sparking a global bird flu pandemic.
Britain is the 13th country in the 25-nation European Union to report a case of a wild bird dying from H5N1.