Birdflu Could Kill 50,000 Britons - Government Adviser

Donaldson said history suggested the bird flu virus could combine with a human flu virus and become easily transmissible.

"Once in a while, every 10 to 40 years, the flu virus mutates into a strain which we haven't got natural immunity to," he told BBC TV. He said a normal winter flu kills more than 12,000 people in Britain.

"If we had a (birdflu) pandemic the problem would be the existing vaccines don't work, we would need a new vaccine and people don't have natural immunity," said Donaldson.

"So the estimate we are working towards is around 50,000 excess deaths from flu, but it could be a lot higher than that -- it depends on whether the strain is mild or serious."

He said Britain was preparing for a pandemic by stockpiling anti-viral drugs which can reduce the severity of attacks and prevent some deaths. He said restricting peoples' movement would not be a priority.

The H5N1 strain first emerged in Hong Kong in 1997, causing the death or destruction of 1.5 million birds and sickening 18 people, killing six.

It re-emerged in 2003 in South Korea, and has now spread to China, Vietnam, Thailand, Laos, Indonesia, Turkey and Romania. H5N1 has infected 117 people in four countries and killed 60, according to the World Health Organization.