LONDON  - The likelihood of the lethal H5N1 strain of the bird flu virus mutating into a form that can be transmitted between humans is "very low", the British government's chief scientific adviser said.

Louise Petrie, laboratory scientist of Scottish Agricultural College Veterinary Services, tests biological samples from a suspect swan at a laboratory in Aberdeen, Scotland, 08 April 2006. The likelihood of the lethal H5N1 strain of the bird flu virus mutating into a form that can be transmitted between humans is "very low", David King, the British government's chief scientific adviser, said. [AFP]

David King was speaking after a dead swan discovered in eastern Scotland this week was found to have the H5N1 strain of the disease, prompting speculation that the virus could spread throughout Britain.

But although the scientist acknowledged that transmission of the disease from birds to humans could trigger a global pandemic, he said it was "totally misleading" to say it was inevitable.

"The pandemic flu that we are now talking about would be in the human population. It is not in the human population at the moment," he told ITV1 television.

"So, yes, the government is preparing for that possibility but I would say it's a very low possibility. I don't believe it's inevitable."

King noted that despite the 100 or more deaths from bird flu, mainly in Asia, widespread human-to-human transmission of the disease had not developed.

And he denied that the swan's discovery meant that bird flu was now in Britain, insisting it was "absolutely not" in poultry and that he was "fairly optimistic" about the wild bird population escaping the disease.

"The one swan does not mean it has arrived here. We need to see more evidence of spread before we can say that is has arrived in the United Kingdom," he said.

Malaysia announced Sunday it was banning imports of birds and eggs from Britain following the discovery.

The mute swan in Scotland had a "very similar" strain of the H5N1 form of bird flu to the one found in scores of birds on the German island of Ruegen in February, Scotland's chief veterinary officer Charles Milne revealed Sunday.

But he said there was no scientific proof to determine how the swan came to be infected.

The discovery has prompted thousands of calls reporting dead birds to a national helpline set up by the environment ministry.