The discovery of a strain of bird flu found in a dead swan in Scotland yesterday brought the potential threat of the deadly H5N1 to Britain for the first time. It also triggered a number of responses which are in place to deal with any outbreak of the strain which can be fatal to humans if they come into contact with it.

A sample from the dead swan tested positive for ?highly pathogenic H5 avian flu?. H5 is a contagious strain and can be fatal to birds.

While further tests are being carried out to see if the bird was infected with the H5N1 strain, the first steps to reduce the danger posed to other birds and people were being put in place. Results from the further tests are expected today.

Once the virus in the swan was identified as a type of H5 avian influenza, a 1.8 mile (3km) protection zone was set up around Cellardyke, a small coastal town in Fife, nine miles from St Andrews, the area where the carcass had been found, according to the European Commission .

The virus will undergo further tests at the Veterinary Laboratory Agency in Weybridge, Surrey to identify exactly which type of the highly pathogenic H5 virus it is.

?We don?t know exactly when that?s going to come through,? said Freda Scott-Park, president of the British Veterinary Association.

What no one knows is how many small flocks of birds there are in the are in the area. Vets will be going into the area immediately to make sure they know exactly where all the birds are. While the waiting is going on there will be a lot of activity going on to make sure the virus doesn?t spread,? said Dr Scott-Park. ?That?s identifying at-risk birds, giving advice to people who live in that area and making sure we all take our responsibilities seriously and act proportionately.?

If the virus is confirmed as H5N1, the exclusion zone will be extended by six miles and movements of birds in the area might be halted, with farmers told to keep their animals inside. Because the virus was found in a wild bird, farmers can probably rest easier that their flocks are not in danger of being culled.

Around the country free range and organic producers have been told for weeks that they should be ready in just such an emergency and tests on poultry farms are likely to be stepped up.

Poultry workers may be offered both seasonal flu vaccine and antiviral drugs to minimise the risk that the virus could mutate into a type more dangerous to humans. The government only completed a register of poultry owners last month and it is not certain it knows where all the farms are since those with flocks of fewer than 50 birds did not have to comply.

But avian flu is not easily spread, requiring extremely close contact with infected birds, particularly faeces.

Culling of wild birds is not an option, since shooting might well disperse flocks further. Culling poultry, if necessary, is likely to be done by gas on large battery farms, and mobile units could be sent round other farms. On some small units however, birds might have to be killed by wringing their necks.

Precautionary measures

The government has powers to vaccinate flocks as a precautionary measure, and many organic and free-range owners have been pressing for just such a move. But ministers are resisting the idea on scientific advice that it is too difficult, and it can take up to three weeks for birds to deliver immunity and some birds require two doses.

Quite apart from the huge practical difficulties, the vaccination will not stop birds being infected and shedding the virus. It might therefore mask the disease.

Two million vaccine doses have been ordered to protect zoo and other exotic birds. Defra said last night: ?There is currently no indication that it is necessary to use vaccines.?

The antiviral drug, Tamiflu, will also be given because it acts, after exposure, as a prophylaxis. Five million doses have been stockpiled so far, in the event of a pandemic, and a total of 14.6m - enough for a quarter of the population; the number predicted to be affected ? will be in place by August.