UK tests have confirmed a case in Romania of a strain of bird flu which is potentially deadly to humans.
Bird flu has spread from South-East Asia
Tests have been carried out on infected birds at the Veterinary Laboratories Agency in Weybridge, Surrey.
On Thursday, the H5N1 strain was confirmed in Turkey, sparking fears avian flu could spread to the UK through migrating birds.
Doctors have warned Britons not to panic, while the government has told farmers to remain vigilant.
'State of alert'
The H5N1 strain has killed more than 60 people in Asia since 2003.
"The results are that it is H5N1 but further laboratory results are required in order to confirm the origin of the virus and the relationship of that with Turkey," said a spokesman from the Department for Environment, Food and Rural Affairs.
Defra has not yet ruled out moving free-range chickens indoors to prevent them coming into contact with potentially infected migratory birds.
Free-range chickens make up 25% of the national flock.
Louise White, of the National Farmers' Union, said: "All we can do is be on a heightened state of alert.
"Biosecurity is very important to UK farming - keeping visitors to a minimum, using lots of disinfectant, keeping places clean and tidy, and not doing anything that might attract migratory birds."
Doctors have stressed that the H5N1 virus has not mutated to be able to jump easily from person to person and fuel a pandemic.
Many of those who have caught the virus in Asia have been poultry workers who have been in close contact with infected birds.
John Widdowson, vice president of the British Free Range Egg Producers Association, added it was not possible to catch avian flu from eating poultry meat or eggs.
Hamish Meldrum, the chairman of the British Medical Association's general practice committee, said: "The main advice is not to panic.
"I'm afraid at this stage there's isn't really any practical thing people can do. They don't need to keep away from birds or anything like that."
He backed government advice for groups such as the elderly and children suffering from diabetes or asthma to have a winter flu jab as usual.
David Salisbury, head of immunisation at the Department of Health, has said the jabs will protect against flu, but not against an "emerging pandemic strain".
However, Dr Meldrum warned that anti-viral drugs being stockpiled by the government were "not an absolute panacea against a potential virus outbreak".
His comments follow research from the scientific journal Nature which suggests that the H5N1 strain may be partially resistant to Tamiflu.
The UK government has ordered 14.6m doses of Tamiflu - enough for 25% of the population.
On Friday, the EU banned all imports of poultry meat, eggs and feathers from Romania and Turkey after a meeting of its vets.
In the UK, birdwatchers, wetlands and wildfowl organisations, and game shooting groups have been asked to look out for large numbers of unusual deaths in species, particularly ducks.