Two of the government's senior scientists are at loggerheads over the risk of a human flu pandemic. As experts in Scotland continued the search for birds infected with the H5N1 virus, confusion reigned in the Department of Health and the Department of Trade and Industry over just how great a risk it represented.

Britain has been preparing for a human pandemic for more than a year and has spent millions stockpiling antiviral drugs and drawing up emergency plans to be put into action if an outbreak occurs.

Yesterday Sir David King, the Government's chief scientific adviser in the DTI, said a human flu pandemic was "not inevitable". That flatly contradicted remarks by the Government's chief medical officer, Sir Liam Donaldson, of the DoH, that a human pandemic was inevitable. Sir Liam has said several times it was a question of "when, not if" a pandemic struck.

Sir David had been questioned by Jonathan Dimbleby in an ITV interview on Sunday about newspaper reports of emergency measures planned by the government.

He said: "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. So, yes, the Government is preparing for that possibility, but I would say it is a very low possibility."

A spokeswoman for the chief scientist said: "Sir David does not believe a human pandemic is inevitable. He thinks there is a low probability of any human flu pandemic now or in the future. It is a question of if, not when. It is not inevitable we will have a human pandemic."

The official consensus, from the World Health Organisation (WHO) last year, said a pandemic would happen but its timing was uncertain. Sir Liam shares the WHO's view.

In a leaked letter which was revealed at the weekend, he warned that in a worst-case scenario up to 100,000 children could die.