Poultry farmers are being told to prepare to move their birds inside in case avian flu hits the UK.
Chickens could be ordered inside if the virus reaches the UK
While it was not inevitable the virus would arrive, the risk had increased, Tony Blair's spokesman said.
EU farm ministers are meeting in Brussels to discuss the spread of the virus, which has now reached France.
UK ministers said it was still not necessary to lock up Britain's 20 million free-range poultry, despite some experts backing it.
The National Farmers' Union said such a move would be a "massive over-reaction".
There are an estimated 200 million birds on farms across the UK and between 10% and 15% are free-range.
Current British policy is that birds would be ordered inside only if the disease was found in the UK.
That possibility has moved a step closer with the news that France has confirmed its first case of the deadly H5N1 virus.
Tony Blair's official spokesman said: "It is common sense that as the incidents of bird flu on the continent geographically get closer, so the level of concern increases.
"We recognise that, and that is why Defra is issuing new guidance today telling poultry farmers that they should prepare plans to bring their flocks in if that is necessary.
"It is still not inevitable that bird flu will come to the UK, but clearly the risk must be higher today than it was."
A Defra spokesman said the original guidance to poultry farmers was being repeated, rather than any new advice being issued.
NFU president Tim Bennett said his union was sure poultry producers would be ready to get birds indoors at short notice once it was needed.
Mr Bennett urged shoppers not to stop buying and eating British chicken, which will remain safe to eat.
Environment Secretary Margaret Beckett agreed, saying it was important "to reassure people that there is no reason to stop eating poultry in the way that they normally do".
She dismissed claims of confusion over who would be responsible for tackling a UK outbreak and said the jobs of the various services had always been clear.
"If you are asking me where the buck stops, you are looking at it," she added.
Professor Neil Ferguson, a mathematical biologist from Imperial College London, thinks the government response is right because solutions must be long-term.
He said the H5N1 virus could be endemic in wild bird populations in Western Europe for decades.
EU farm ministers are debating the introduction of a preventive vaccination against bird flu.
However, the government has said this would be hugely expensive and could be confusing because it could only prevent symptoms in birds, not the disease itself.
Nine dead swans have been tested for signs of infection, after reports from the public - two each were from Bury St Edmunds, Winchester and Preston, while individual birds were found in Shrewsbury, Thirsk and Hertfordshire.
A Defra spokesman said the Veterinary Laboratories Agency had confirmed that all nine had tested negative for bird flu.
Several pairs of swans at Abbotsbury Swannery, a nature reserve in Dorset, have been moved about 20 miles inland because of the threat of avian flu.
And nearly 11,200 commercial keepers with 50 birds or more have so far registered on Defra's central database ahead of the February 28 deadline.
Peter Bradnock, the chief executive of the British Poultry Council, told the BBC his industry was concerned but well-prepared.
In the event of the virus spreading to a UK poultry farm, the disease would be spotted quickly, the farm isolated and hopefully the infection contained, he said.
The H5N1 strain has killed dozens of people in Asia, the vast majority following very close contact with sick birds.
But some scientists fear it could mutate so that it could be passed easily from person to person.