Obesity is the price we pay for our evolutionary success. This new health scourge, caused by our ability to store fat so efficiently, is a disease which may ultimately prove more devastating than the TB and diphtheria epidemics of the last century. As we report today, it will leave thousands of children and teenagers facing diabetes, a condition which carries with it all kinds of health hazards, including heart disease and blindness.

There is no vaccine for obesity, no miracle pill or gene therapy to prevent its onset. The only things which work are long-term lifestyle changes: a healthy diet and plenty of exercise.

How far can a government transform the health of a nation? Ministers prevaricate, caught between their desire to prevent the 'ticking timebomb' of obesity from wiping out the benefits of their health reforms and the fear that they will be accused of promoting a 'nanny-state'. We are left with a sterile debate over who is to blame for the rise in 'couch-potato' lifestyles.

Amid a raft of well-meaning but so far ineffective government measures, sport in schools is being shamefully neglected. Yet it is the one area where Ministers could really make a difference. In Sweden, which recognises that early action keeps children healthy in later years, the school working day has been altered to allow pupils to turn up at 8am for half an hour of exercise, followed by an hour in the afternoon. They enjoy, on average, 10 hours of sport a week. In Britain, the aspiration is merely that 75 per cent of children should have two hours of sport a week by 2006. If we're serious about fighting obesity and the chronic illness it breeds, more activity for children must be top of the list.

Sport must no longer be an add-on, squeezed into the national curriculum as an afterthought. Tony Blair, who takes pride in his own physical fitness, must make some radical changes to both the school day and its curriculum. If that means less time for endless testing, children may find that they are winners twice over.