The chief medical officer's advice to take enough exercise to get up a sweat at least five times a week, accompanied by the reassurance that energetic housework rather than pounding the pavements will do, was well-intentioned. Obesity, it is reckoned, could soon be costing the country £10bn a year. Our sedentary lifestyle makes us more vulnerable to other forms of ill-health too. As a handsome part of the profits of the keep-fit industry comes from failed good intentions - £200m a year is paid in unused gym subscriptions - encouraging easier, and cheaper, forms of exercise such as walking benefits everyone.

But while it is reasonable for the government to ask us to take more responsibility for our own health, it is also its duty to make it possible. Many still find it too scary to cycle in cities, and despite legislation 200 playing fields have been sold off in the past five years. There are still too few safe, local, outdoor areas in urban neighbourhoods, while schools are only slowly introducing exercise opportunities for the sportophobic.

Sir Liam Donaldson's advice also ducked the real issue. Obesity is disproportionately a disease of poverty, affected by culture and diet, as well as opportunities for exercise. But more than any of those things, recent American research suggests that there is an important psychological element: those who feel least in control of their lives are most vulnerable. More, there is now evidence that the same people actually find it harder physiologically to lose weight. Distant exhortation will have least effect where action is most needed. The government needs to pluck up courage, see off the charge of the nanny state and move from exhortation to intervention.