A flu pandemic is inevitable, the World Health Organization says

The measures are likely to be included in the government's contingency plan, which will be published in the spring.

Ministers have been warned an outbreak of a deadly flu virus is long overdue - the last one was in 1968.

Experts fear Avian flu, which has killed 32 people in South East Asia, could mutate to allow it to be passed from person-to-person.

Any contingency plan must include provision to stock up on these drugs, without them we would be in real trouble Professor John Oxford

The virus can only be passed to humans by infected birds at the moment.

But it is thought the strain of the virus could easily acquire the characteristics of human flu and become much more infectious.

Last year, the World Health Organization said an flu pandemic was "inevitable" and countries across the world should start preparing.

There were three flu pandemics during the 20th century. The worst one in 1918 killed up to 50m, including more than 200,000 in the UK.

The Asian flu outbreak in 1957 and Hong Kong pandemic 11 years later both killed 1m each.

The Department of Health's UK Influenza Pandemic Contingency Plan will set out how an outbreak in Britain will be handled.

Some countries such as Japan, Holland and Australia have already started buying antiviral drugs, which work by reducing the symptoms and the risk of a carrier passing on the virus.

Professor John Oxford, professor of virology at Queen Mary's School of Medicine, said these would be the best first-line of defence as it would be months after the start of a pandemic before a vaccine could be developed to give people immunity.

Drugs

"They would blunt the first wave of the outbreak. Any contingency plan must include provision to stock up on these drugs, without them we would be in real trouble."

Professor Oxford estimated about �50m would have to be spent on building up reserves for up to a third of the population.

A Department of Health spokesman said the government was looking at what sort of quantities of antiviral drugs should be gathered.

But ruled out mass evacuations of cities and towns to limit the impact of an outbreak.

"The last thing you want to do is get people together in one place that would make it easier for the flu to be passed on.

"It is far more likely that people will be told to stay at home so they don't come into contact with others."