Veterinary officials ordered all free-range birds within a three kilometre zone of the dead mute swan to be brought indoors, but they insisted that a wider ban on keeping domestic poultry outside was not yet necessary.

Instead, they asked poultry farmers within a 2,500 square kilometre "wild bird risk" area in Scotland - containing 3.1 million birds of which 260,000 are free range - to voluntarily bring their birds under cover, wherever possible.

There are fears the bird contracted the virus in Britain, since mute swans are non-migratory. Yesterday dead swans found in Glasgow's Richmond Park, and at Portglenone and Moira in Northern Ireland, were being tested for avian flu.

Health officials tried to calm public fears, saying that the risk to humans was minimal and that it was only possible to catch bird flu by close contact with living birds or their droppings.

There is a bigger risk of infected wild birds passing on avian flu to free-range chickens, geese and turkeys, but officials believe that a nationwide ban on keeping poultry outside would at this stage be too draconian.

"On the basis of a preliminary risk assessment it has been concluded that a nationwide poultry housing requirement would be disproportionate," said a joint statement from the UK and Scottish chief veterinary officers.

"We are urgently considering whether there is a need for any regional measures in addition to those that have already been put in place."

The mute swan died at least five days ago near Cellardyke in Fife and was badly decomposed by the time it was tested for the H5N1 strain of avian flu by scientists at the Government's Veterinary Laboratories Agency in Surrey.

Some countries, such as the Netherlands, have already ordered all domestic birds indoors and Bob McCracken, past president of the British Veterinary Association, said that the day of a national ban on keeping birds outside was getting closer.

"The order of the day is to minimise contact between wild birds that may be infected, and domestic birds. The most simple way of doing that is to remove them indoors," he said.

"There is no doubt whatsoever that we're getting much closer to the day when moving birds indoors will become necessary.

"If I were a poultry keeper, no matter how big or small, I would wherever possible be moving my birds indoors before it becomes mandatory to do so," he said.

Experts assume that other wild birds in Britain are already infected with the H5N1 strain of bird flu. "I find it very difficult to accept that we could have a single bird anywhere in the UK infected with this virus and not to have passed it on to some other birds in its immediate vicinity," Mr McCracken said.

"I would start from the assumption that there is a small pool of birds in the Fife area that are infected, and that they could pass the virus on to other birds," he added.

Other species are also at risk of bird flu, such as domestic pigs and pets, and scientists warned members of the public to keep dogs on leads and cats indoors.

Alan Hay, director of the Medical Research Council's World Influenza Centre at Mill Hill in London, claimed that cats could become infected by wild birds and pass on the virus to their owners. "The area of concern at the moment is to understand the extent of infection in birds and the likelihood that a cat might eat an infected bird and become infected, and then be a source of potential infection for the family," Dr Hay said.

There is also a risk of avian flu being transmitted to domestic pigs, which are known to be capable of being simultaneously infected with avian and human strains of influenza.

"There have been a number of cases in Asia where pigs have been shown to be infected by the virus but to date there has been no evidence that the infection has established itself by spreading from one pig to another. It is a major concern to us given the possible scenario that such an animal could provide an intermediate host for the emergence of a virus with a greater capacity to infect people," Dr Hay said.

The greatest fear is that H5N1, which globally has killed about half of the nearly 200 people it has infected, could mutate into a more transmissible virus.

"We are going to study the various hypotheses with those concerned. I am anxious to protect the health of our fellow citizens but also to draw the lessons of experience and do everything with the greatest possible consensus," he said.

Last month France's Social Affairs Inspectorate (IGAS) concluded that the 1991 Evin Law which obliges restaurants and other public places to have separate smoking areas is being "badly applied," and recommended it be superseded by an outright ban.

Health Minister Xavier Bertrand said at the time that "today's status quo cannot hold."

A poll last week showed that 78 percent of the French are in favour of a total ban on smoking in public places.