At the risk of sounding like Corporal Jones in Dad's Army, the response to the news that the bird flu that killed thousands of turkeys in Suffolk was the serious H5N1 strain should be: Don't panic. Bird flu is one of those risks that modern risk-averse societies have some difficulty coming to terms with. Our lust for certainty is not satisfied by the unknown chances of a certain event, namely the next flu pandemic. That there will be a flu pandemic - a global epidemic - is certain. But we do not know when it will be, or how virulent it will be, which are the facts that really matter.

The importance of H5N1, which has been monitored since 1997, is that it is a severe strain of bird flu that has "pandemic potential", according to the World Health Organisation. In other words, it is a bird virus that has the potential to change into a form that is easily transmissible between humans. At the moment, it can infect humans only by direct physical contact. That is why the outbreak in Suffolk poses a low risk to anyone other than turkeys. The affected birds have been destroyed and in any case the virus is killed by cooking.

The world is still waiting, then, for this - or another - strain of bird flu to change into a form that can be transmitted between humans in the way that normal flu is, that is, by coughing or sneezing. The outbreak in Suffolk does not alter the odds of this evolution occurring. When that happens, it will happen in a developing country where people live with their poultry and pigs and the pool of viral material is greatest. The significance of the Suffolk outbreak is twofold. One, it underlines the extent and persistence of the H5N1 strain around the world. Two, it points up the weakness of the official systems for infection surveillance and control.

When the flurry of feathers on the turkey farm dies down, however, the real worry remains the risk that a bird flu virus will somewhere, far from Britain, transform into a human pandemic form. That is the real eventuality for which governments need to plan. Wherever it starts, it will probably spread around the world in less than three months. There were pandemics in 1918, 1957 and 1968, when most international travel was by ship, and the illness encircled the globe in six to nine months. Of those three pandemics, the first was easily the worst, killing up to 50 million people worldwide; the later ones caused two million and one million deaths respectively.

Some scientists argue that, as the H5N1 strain has not transformed into a human-transmissible form in 10 years, it is unlikely now to do so. But one strain will transform eventually, and we have no idea how deadly it will be.

All that governments can do is to stockpile anti-viral medicines that may or may not be effective and to "stockpile" the capacity to produce vaccines when the pandemic virus itself emerges. This Government is doing both, after a hesitant start. The outbreak of bird flu on a turkey farm in Suffolk may not be a danger to human health, but it serves as a useful reminder of a potential danger that still lurks elsewhere in the world.