In the United States, some patients with tuberculosis are having parts of their lungs surgically removed. This is a crude treatment belonging to the pre-antibiotic age. But the individuals concerned have acquired a strain of TB so resistant to drugs that only radical measures offer them hope of survival.

Infectious diseases have returned with a vengeance. The plight of these patients is a sign of the future when more diseases are likely to prove unresponsive to the antibiotics that have saved millions of lives since the Second World War.

Yesterday, Professor Roy Anderson of Oxford University, broadened the grounds for concern. He warned that widespread use of vaccines could lead to viral mutations, threatening even those who have been vaccinated.

These problems are a challenge to pharmaceutical companies, which have a financial incentive to find fresh ways to combat the new foes that nature throws up. They are seeking new antibiotics by designing or discovering chemical compounds that kill dangerous bacteria.

Yet, for now at least, science seems to be losing the battle.We are running out of effective drugs. So we should be more careful with those weapons that remain effective. Britain is a beacon of good practice: drug-resistant TB has so far been avoided thanks to a National Health Service which ensures that patients complete prescribed courses of treatment. Antibiotics can be obtained here only with a prescription, so their use is less extravagant than elsewhere, further reducing the danger of drug-resistance developing.

But general practitioners, bombarded with advertising, are sometimes too willing to prescribe new drugs that should be reserved for the future, rather than persisting with older alternatives which remain effective. They are also prescribing far more antibiotics than ten years ago, frequently without being sure that a patient actually has a bacterial infection: only a minority, for example, take a swab before prescribing for a sore throat. Patients often fail to complete a course of treatment. All these actions are likely to hasten the day when bacteria mutate and can beat existing drugs.

Drug licensing should be tightened. Last month, the US authorities set an example by rejecting an application to sell Zovirax over the counter as a treatment for genital herpes. A prescription is required because the authorities fear that over-use of the drug would lead to resistant forms of the virus developing. Yet this anti-viral drug, unlike antibiotics, is still available over the counter in Britain as a cream for coldsores.

Doctors, patients and the Government must change practices established in a period when infectious diseases seemed to be a scourge of the past. Otherwise we risk finding that the medicine bag is empty.