The government has awarded two companies multi-million pound contracts to produce a vaccine against the deadly strain of bird flu for humans.
Healthcare workers are one of the groups who would be given the vaccine
The contracts for 3.5m doses of the vaccine against H5N1, worth £33m, have been given to pharmaceutical firms Chiron and Baxter.
The vaccine will be given to key groups such as health workers in the event of a pandemic.
The announcement comes as turkeys on a farm in France are tested for bird flu.
H5N1 has so far affected 170 people in south east Asia and Turkey, killing 90.
In Europe, the flu strain has so far only been confirmed in wild birds. If the French farm birds do have H5N1, it would be the first time the virus had affected domestic poultry in Western Europe.
'Can't be clear'
The UK government says it has ordered the supply of the H5N1 vaccine, which will be delivered by October this year, as a contingency measure.
Both companies' vaccines are still under development.
Health Minister Rosie Winterton said: "Building a stockpile will allow us to carry out more research and could be offered as a possible first line of defence for NHS workers whilst the exact vaccine to match the pandemic flu strain is manufactured."
But Ms Winterton admitted the vaccine might not be effective if the pandemic strain of flu was significantly different to the H5N1 strain being seen now.
Ms Winterton, who is attending a meeting of EU health ministers in Vienna, told BBC Radio 4's Today programme: "It is certainly true that if the H5N1 virus developed into a virus that could be passed between humans, you couldn't be absolutely clear that an H5N1 vaccine would be appropriate.
"If a human pandemic does develop, we would have to look at that point at the virus and then develop a vaccine from that."
She added: "There is no guarantee that a vaccine would be appropriate in those circumstances."
Ms Winterton stressed there was no evidence that the H5N1 strain had affected either wild or domestic birds in the UK.
Other countries, including France, Canada, Australia and the US, have also announced they will be making or have made arrangements to purchase limited quantities of H5N1 vaccine.
The UK government has also asked manufacturers to tender for a "sleeping contract" to produce 120 million doses of a vaccine, once the exact make-up of a pandemic strain is known.
It has also ordered 14.6 million batches of the Tamiflu antiviral drug - enough for 25% of the population - which reduces the severity of bird flu symptoms.
But Shadow Health Secretary Andrew Lansley said: Shadow Health Secretary Andrew Lansley accused the government of being "woefully complacent" in its plans to deal with bird flu and a pandemic.
He said: "There are still essential measures like the acquisition of gloves, masks and syringes, which other countries have done but we have not."
Chiron, one of the companies awarded a UK contract, had its Liverpool factory shut down for six months in 2004 because of concerns its flu vaccines were contaminated.