The scenes are likely to keep epidemiologists awake at night. Russian vets, wearing masks and white protective clothing, incinerating the carcasses of thousands of slaughtered birds on the doorstep of Europe.

Avian influenza, or bird flu, has been endemic in Asia in recent years where it has infected millions of fowl and caused around 60 human deaths. Its spread first to Siberia and then west to the Ural mountains confirms many scientists' predictions that the highly infectious disease would be nigh impossible to control.

"This flu will not go away any time soon," said Neil Ferguson, a professor of mathematical biology at Imperial College London. "There is nothing really to stop it spreading. It is entirely likely that it will spread across Europe and into the Americas."

Though the government insists the risks of the highly contagious viral disease arriving in the UK are still low, authorities are on alert. The Department of Health and Department for Environmental, Food and Rural Affairs have guidance and contingency plans for dealing with the virus on their websites.

Of the current forms of bird flu, the most infectious is a highly pathogenic influenza A virus known as H5N1. There are serious concerns that the virus could devastate poultry production in this country. Two years ago, 28m farm birds were killed in the Netherlands following an outbreak, and as of today the country has ordered all poultry farmers to move their birds indoors to cut the risk of contact with wildfowl.

British authorities warn that such measures would be much more disruptive in this country, where 25% of poultry farming is free range compared with only 1% in the Netherlands. The environment minister, Ben Bradshaw, has so far ruled out a similar move in Britain saying scientific advice does not justify it.

"If it gets into the domestic poultry industry it would cause mayhem," retired microbiologist Professor Hugh Pennington told Guardian Unlimited. "Clearly it would have an economic impact and would create panic. Drastic measures would have to be taken."

Organic farms, with their chickens outdoors most the time, would be particularly hard hit, he warned, and so too would poultry workers. The disease has been shown to spread to people in close contact with infected birds.

"The protection of workers will be a real issue. I would not put too much stock in masks as a protective measure," Prof Pennington said.

The British Poultry Council acknowledges that any outbreak, however quickly confined, would have huge consequences on people's perceptions of the safety of fowl products.

Yet the real fear is not the welfare of poultry but a potentially devastating impact on human health. To date, the virus has only passed from bird to bird and, occasionally in Asia where chickens are more likely to roam in towns and villages, from bird to human.

Scientists worry that the virus will mutate into a form that could be passed from person to person. That could happen in a person, or possibly a pig, infected with the bird virus and coincidentally with human flu. The viruses could exchange genes creating a hybrid that passes from human to human with catastrophic consequences.

Government scientists predict a quarter of the British population could become infected, and a similar number would have to take time off work to care for them. The Department of Health's contingency plan states anywhere between 21,500 and 709,000 deaths could be expected in Britain from a bird flu pandemic. The worldwide death toll could be as high as 200 million, according to some experts.

"Around 40 million people died in 1918 Spanish flu outbreak," said Prof Ferguson. "There are six times more people on the planet now so you could scale it up to around 200 million people probably."

In March the government announced it was spending £200m on the anti-viral drugs to treat 14 million people. Anti-virals do not prevent people becoming infected but could reduce the effects. Last month the government also said it would buy 2m doses of vaccine for key workers, though it will take around six months for it to arrive. The problem is that it is difficult to produce the right vaccine before the strain of an outbreak is known.

"It is proving hard to find an effective vaccine for the H5N1 strain," said Prof Ferguson. "We have done considerably more than other countries but if it happened tomorrow we would be poorly prepared."

As part of its preparations for a UK outbreak, the Department of Health will send out information packs to GPs and other primary care staff next month. The packs will include a copy of the chief medical officer's 50-page technical guide, Explaining Pandemic Flu and Family Advice.

Experts say a flu pandemic would spread very quickly and question whether, despite public assurances, the government is ready.

"At the end of the day it will be very difficult because it will come down to a lot of difficult judgments," Prof Pennington, who retired from the University of Aberdeen in 2003, said. "There will be people infected who don't know it and there will be people who claim to have flu who do not have it. With limited stockpiles of medicines, it will be a big issue of how do we administer them and to whom?

"The lab service will be very stretched when it gets going. We have not been putting much investment into virology labs and the Health Protection Agency, and there is no slack in the system.

"There will be no problem about spotting it when it comes. There question is are there enough specialists? You can get away with it most of the time but like with foot and mouth, as soon as we were tested seriously we ran out of specialists on day two."

The 2005 annual report of the HPA, formed in 2003 when the Public Health Laboratory Service merged with the National Radiological Protection Board, refers to "a financially challenging year" with "unfunded" cost pressures of around £3.6m. In the financial year to March it reported a £951,000 deficit, down from £3.1m the year before.

Prof Ferguson believes health authorities have taken the wrong approach to bird flu.

"All the planning done to date is about mitigation and treating," Prof Ferguson, who published a paper earlier this month about modelling the spread of bird flu, said. "The planning is about mitigation and that at best is going to save around half the number of lives that could be lost in a pandemic. Containment would stop around 95% of deaths."

Prof Ferguson's modelling studies suggest that an outbreak could spread around the world in three months but if it was detected in its infancy, with less than 50 cases, it could be contained using antiviral drugs. This could be achieved, he said, if an international stockpile of 3m courses of antivirals was available to give jabs to anyone who lives near to or who has come into contact with the infected people.

A Department of Health spokeswoman said more work was being carried out on how best to use antiviral drugs and results would be published "shortly". She said drug administration strategies would depend upon the strain of flu involved in an outbreak so the correct section of the population could be targeted.

She rejected claims that agencies such as the HPA do not have sufficient resources to cope.

"We completely disagree with that. We have looked at the role of the HPA in the plan and set out what they have to do. The whole point of drawing up plans is to make sure we are as prepared as we can be."