Farmers' groups have told of their "surprise" at comments by the chief scientist that he expects bird flu to arrive in the UK and remain for years.
Prof King has said bird flu could stay in the UK for "five years plus"
Professor Sir David King, the government's chief scientific adviser, told the BBC it may become "endemic" and remain for "five years plus".
He also ruled out using the existing vaccine against the H5N1 strain.
The National Farmers' Union said it "simply did not accept" his view that the virus would become prevalent.
"If someone is saying we are going to see this endemically within the UK commercial flock that is a surprise," the NFU's chief poultry adviser said.
The NFU was following scientific and veterinary advice on the question of vaccination, chief poultry adviser Maria Ball said.
But the Soil Association said it was "mystfied" and "dismayed" by the decision not to vaccinate.
It called for the use of "ring" vaccination - when poultry close to any outbreak are inoculated.
"They have got to bring in every weapon in their armoury," said the association's Robin Maynard.
He said he had a sense of "deja vu", likening it to the 2001 outbreak of foot-and-mouth disease.
"The end result was 11 million animals slaughtered and £8bn cost to the tax-payer.
"We just don't want to go down that barbaric, medieval route."
But mass vaccination of British poultry in the event of a bird flu outbreak had not been ruled out, Environment Secretary Margaret Beckett said on Monday.
However, Mrs Beckett has questioned the vaccine's effectiveness in preventing the H5N1 virus spreading.
The government is understood to be holding talks with Chinese scientists who are developing a new vaccine, which it is hoped will be more effective.
Prof King said the existing H5N1 inoculation would mask signs of the virus in birds but not prevent its spread.
Rare breeds of birds kept in zoos would be the only cases where vaccines would be feasible. The inoculation of organic or free range birds would not be recommended.
The vaccination of nearly a million free range ducks and geese has begun in south-west France.
In the UK, people with 50 or more poultry must register with the government before midnight on Tuesday.
Prof King told BBC News: "I would anticipate that avian flu will arrive at some point in the UK.
"We also have to anticipate that it will be here for five years plus. We are talking about the possibility of this disease being endemic here in the UK."
BBC environment correspondent Sarah Mukherjee said Prof King's comments seemed to "fly against the spirit of what we have heard from all sorts of government scientists and ministers".
But she said he may be envisaging sporadic outbreaks that would be prevented from spreading beyond small areas.
Free-range poultry farmer John Widdowson, from Tiverton, Devon, said Prof King's comments were "no surprise at all".
"But I still think we have got a good chance of keeping it out of poultry flocks. We have had lots of time to prepare for this," he said.
"This doesn't need to be a catastrophe."
But organic poultry farmer Ritichie Riggs, from Holsworthy, Devon, branded Prof King's comments as "irresponsible", while the decision not to vaccinate had left him "demoralised".
"They don't care about the flocks, they are not farming people, they don't care about the animals," he said.
"We are just going along exactly the same route as they took with foot-and-mouth disease," he said.