The Government's chief scientist today led calls for calm over Britain's first confirmed case of H5N1 bird flu, insisting that one dead swan does not constitute a crisis.

Sir David King also defended the eight-day delay in pinpointing the potentially lethal strain in the decomposed remains of a swan found in Cellardyke, Scotland, saying it was remarkable that a result was obtained at all.

Tests are continuing on the bodies of 14 other birds also suspected to be carrying the disease: it is considered unlikely that the Cellardyke swan is an isolated case.

Supermarkets today reported that there had been no immediate fall in sales of chicken or eggs. They will be told later today whether products from farms within a 965 sq mile 'high risk' area must be labelled accordingly.

All 175 registered poultry farmers in the region, which stretches north of Dundee and Perth, must bring their flocks indoors or take measures to prevent them from mingling with wild birds. Tighter restrictions on transporting livestock are in place in a 1.8 mile radius (3km) protection zone around the fishing village.

Sir David, who was among the senior civil servants called to a meeting of the Government's emergency panel Cobra yesterday, said that he believed Britain was better prepared than any other nation to deal with the outbreak because of the lessons learned from foot-and-mouth.

"I wouldn’t describe this as a crisis. I don’t think that one dead swan is a crisis," he told the BBC today.

He said there was no danger posed by the eight-day delay between the Cellardyke swan's discovery and the eventual confirmation that it was carrying the feared H5N1 strain. There has been criticism that the time taken has increased the risk of other birds being infected.

Sir David said: "Governments don’t act within an infinite budget and keeping people operating 24/7 is something that would be only brought into play once we are dealing with a crisis," he said.

He added he was not discouraged by the eight days it took to finish testing the dead swan, adding that the carcass had been in an advanced state of decay.

The bird is understood to be a mute swan, a native species that does not normally migrate long distances, suggesting that it contracted the virus from another bird arriving from the Continent

"Some of us think it’s quite a remarkable achievement that the test was conducted at all," Sir David added.

Alex Salmond, leader of the Scottish National Party, said that Britain needed to improve its reaction time to future discoveries of potential cases.

He said: "We must be able to act quickly and efficiently if we are to manage this situation effectively."

Professor John Oxford, scientific director of Retroscreen Virology Ltd and Professor of Virology at St Bartholomew’s and the Royal London Hospital, said it was important not to panic.

He said: "The danger to humans at this stage is virtually zero. The danger for chickens and turkeys in the immediate area will be much higher."

The current outbreaks of pathogenic avian flu began in south-east Asia in mid-2003 and is now considered endemic in many parts of China and south-east Asia. It spread to Europe in January when two Turks were found to have been infected with H5N1.

There have been a total of 191 confirmed human cases of the H5N1 strain of bird flu reported to the World Health Organisation to date and 108 human deaths.

The major fear is that the virus could mutate into a form transmissable between humans, triggering a pandemic. The 1918-19 flu pandemic was triggered by an avian strain that mutated, and killed up to 40 million people.

Jeremy Blackburn, an executive director of the council, said that annual poultry retail sales were worth £3 billion, with 87 per cent consumed domestically and exports last year amounting to £375 million. "We don’t expect to see any dramatic shift in sales because of a case of avian flu in one wild bird," he said.

There were reports today that T In The Park, Scotland's biggest music festival, could fall foul of the outbreak. The concert, featuring The Arctic Monkeys, Franz Ferdinand and The Strokes, is due to be held next to a huge poultry farm in Balado, Kinross - 35 miles from Cellardyke.

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