We are at phase five out of six – a flu pandemic is “imminent”. What does that mean for Britain?

Business as usual, for the moment. The decision by the World Health Organisation (WHO) to upgrade its threat level comes after sustained outbreaks of the new H1N1 flu strain in Mexico and the United States, but is not expected to affect daily life in Britain. Although eight isolated cases have been confirmed in England and Scotland, all have been diagnosed in people who have travelled from Mexico, and there is no confirmation that the virus has spread farther in this country.

What would it take to get to phase six?

More evidence of “increased and sustained transmission” between people in more than one continent, according to the WHO. As new cases emerge, with or without ties to Mexico, international experts say that it is impossible to predict when we might move to phase six, which would be a declaration of a pandemic.

What happens then?

The Department of Health says that declaring a pandemic would be a “serious development”. However, the WHO alert levels reflect an international situation, and any action taken in Britain would be based on the situation here. The Government has its own set of four national alert levels for use in this situation, depending on the severity and extent of the illness. It is already issuing advice through a large public health campaign and is increasing stocks of antiviral and antibiotic medicines. Scientists are analysing the virus in an effort to find a possible vaccine.

Isn’t all this a bit unnecessary?

Flu is a familiar seasonal illness that can claim up to 12,000 lives from infections or complications in a bad year. But outside Mexico the new H1N1 strain seems to be a relatively mild virus with only one person – a Mexican toddler who had travelled to the US – dying from it. However, there are fears that it could mutate and overcome many people’s immune systems. It is possible that the current outbreaks of infection could peter out, at least outside the traditional winter flu season, only to return again in waves as the virus emerges in new, more dangerous forms. At the moment, most of the public health measures are precautionary. Infections are being dealt with on a case-by-case basis and most people remain unaffected. In the event of a pandemic, however, it is estimated that up to half of the population could become ill, with up to 750,000 deaths.

Britain is considered well prepared, even for the worst possible outcome. How do we know?

Along with holding extensive stockpiles of medication and taking other measures, the Government held a large exercise, codenamed Winter Willow, in January and February 2007 to test its ability to manage a pandemic. That was designed to evaluate the way in which the country’s infrastructure, including health, transport, education and food distribution, would keep working during an outbreak. A Ministry of Defence document, which was obtained under the Freedom of Information Act, suggested that a pandemic would generate “unprecedented levels of public fear, stress and panic”. However, the detailed results of the Winter Willow exercise have not been placed in the public domain.

How ready is British business?

About half of businesses claim to have plans in place for dealing with a crisis and only a third claim to have continuity plans for coping with large staff shortages, according to the Business Continuity Institute. There are also fears that the recession has affected the amount of money spent by companies on emergency planning over the past year. However, all FTSE 100 companies are thought to have well-thought contingency plans as a result of previous fears over H5N1 avian flu.

And what about other walks of life?

In the case of widespread illness or threat of transmission, it is expected that affected schools would close (as has happened already in Devon), and people with flu symptoms would be asked to stay at home. Antivirals or vaccinations will be given as a priority to healthcare workers, at-risk groups (people with respiratory disease, diabetes, heart disease and other serious conditions) and children.

Hospitals could close A&E departments or divert some services, while employers might be asked to stagger working hours to prevent overcrowding on public transport.

Specialist advice has also gone out to prisons, police and other public services in an effort to minimise any chaos.

But the Government says that it is not helpful to close borders, and it is not expected to cancel sporting events or other mass gatherings.

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