Millions of doses of drugs to ward off a flu pandemic are to be stockpiled, the government has announced.
Nearly 50 people have died from bird flu in south east Asia
It said without the antiviral drugs an outbreak could kill 50,000 in the UK.
Experts say a pandemic is inevitable and will probably emerge in Asia if bird flu mutates with human flu, creating a highly infectious new virus.
The UK Influenza Pandemic Contingency Plan also includes quarantine measures, as well as arrangements for the emergency services.
Concerts and football matches could both be banned and travel restricted in the event of an outbreak to stop the virus spreading.
But the government decided against buying up vaccines as ordinary flu vaccines will not be 100% effective because the strain which would be responsible for any future pandemic has not emerged yet.
It could take up to six months to develop a vaccine once a pandemic has started.
Instead, the Department of Health is to stockpile 14.6 million doses of the antiviral drug Tamiflu, which is made by Swiss drugs firm Roche and works by reducing the symptoms and the risk of a carrier passing on the virus, at a cost of £180m.
It will be enough for a quarter of the population - the World Health Organization's recommended level.
Health officials will be the first in line for the drugs, with the remainder being handed out to whichever part of the population is deemed most at risk.
PLANS IN OTHER COUNTRIES
US - Has been stockpiling antiviral drugs and placed orders for 4m vaccine doses
Italy and France - Both placed orders for 2m vaccine doses
Canada and Australia - Have been buying enough antiviral drugs to cover a quarter of the population
Japan and Holland - Also purchasing antiviral drugs but not on the same scale as others
Several countries, including Canada, the US and Australia, have already started building up reserves of the drugs.
Other countries have also placed orders for a vaccine.
Chief Medical Officer Sir Liam Donaldson said the plan had been published as it must be assumed the government would be unable to stop a future flu pandemic reaching the UK.
"When it does, its impact will be severe in the number of illnesses and the disruption to everyday life.
"The steps we are setting out today will help us to reduce the disease's impact on our population."
Experts have become increasingly worried over recent months about the threat of a pandemic.
There were three flu pandemics during the 20th Century. The worst one in 1918 killed up to 50 million, including more than 200,000 in the UK.
The Asian flu outbreak in 1957 and Hong Kong pandemic 11 years later both killed 1 million each.
KILLER FLU PANDEMICS
1918 Spanish flu killed 50m
1957 Asian flu killed around 1m
1968 Hong Kong flu killed 1m
And fears of a new pandemic were heightened a month ago after scientists said they believed the bird flu, which has killed 46 people in south east Asia, had been passed from human to human for the first time.
Leading UK expert John Oxford, professor of virology at Queen Mary's School of Medicine, said: "If the flu does arrive we will have to throw the book at it."
But he said the public should not become too alarmed and could take comfort that the government was putting a plan in place now.
Professor Pat Troop, chief executive of the Health Protection Agency, said it was a matter of when, not if, the flu would strike.
"We do not want to cause panic but we have to take it seriously.
"We have to do this planning and also stockpiling and if it does happen we will have to put in quite tough public health measures."
A WHO spokeswoman said it was a "good idea" to start stockpiling antiviral drugs but said there was still work that could be done on vaccines.
"You can prepare the ground. There are licensing hurdles to be scaled and there is research that can be done to see what can provoke an immune response so that it will take as little time as possible when the time comes."
Both the Tories and Liberal Democrats said the plans were too late and the government should have acted months ago.