Leading article: Your weight. Whose fault?

If you throw food away, it is your fault that the world's poor are starving. If you eat too much food, it is your fault that you are fat. Two messages from the Prime Minister and the Leader of the Opposition last week brought into focus the dichotomy between government action and personal responsibility.

Gordon Brown, speaking to journalists on the plane to the G8 summit in Japan, said that "all of us" have a role in reducing world food prices by cutting our food waste. While David Cameron, speaking in Glasgow East, where there is a by-election next week, said: "We talk about people being 'at risk of obesity' instead of talking about people who eat too much and take too little exercise." As with poverty, alcohol and drugs, he said, "social problems are often the consequence of the choices that people make".

They are, of course, both right. And both wrong. Mr Brown struck a popular chord by expressing disapproval of the throwing away of food. We were delighted that he should endorse an Independent on Sunday campaign launched a few months ago when we reported that consumers throw away one-third of all the food they buy. There may be the slightest tinge of presbyterian sanctimony in his – and our – moral censure of such profligacy, but such disapproval is neither wholly irrational nor wholly derived from folk memory of being made to "eat up" because children were starving in Africa. Avoiding waste is now part of the green plan for the future: humankind can no longer afford to be careless with the Earth's resources.

But that is where Mr Brown went wrong, because the sustainable use of food, water and energy requires government action to give individuals incentives to change behaviour. The Prime Minister can hope that British households will spontaneously rediscover the virtues of thrift and menu planning, but that would have a negligible impact on world food prices. In any case, there is a paradox here that illustrates the wider issue. Food waste in Britain is blamed on food being too cheap while problems in poor countries are blamed on it being too expensive. We have some sympathy, therefore, with Sir Terry Leahy, the Tesco boss interviewed today by Dominic Lawson. Habits such as wasting food have hardly been created by supermarkets, whatever their other culpabilities.

And if they have not been caused by governments or businesses, there is only one point to which primary responsibility should be attached, and that is the individual. Mr Cameron was astute, therefore, in seeking to redress the balance, a balance that had been allowed to get out of kilter by a Government that too often gives the impression of seeking to micro-manage human behaviour. In his speech in Glasgow, he said: "We as a society have been far too sensitive. In order to avoid injury to people's feelings, in order to avoid appearing judgemental, we have failed to say what needs to be said." Our political system and our public sector, he said, refuse to "make judgements about what is good and bad behaviour, right and wrong behaviour".

He has a point. Just as Tony Blair had a point when he said almost the same thing 15 years ago. It is worth saying, clearly and emphatically, that some ways of bringing up children are better than others; that staying at home on sickness benefit is bad for your health; that people should take more exercise; and that everyone should be more polite. But Mr Cameron is playing a dangerous game by saying that right and wrong are words that we "scarcely dare" to use any more. He is playing to a gallery that believes that "political correctness" is a conspiracy by the ruling class literally to demoralise society. It ain't so. There is a good reason for being "sensitive" about blaming fat people or poor people or lone parents for their disadvantages. Sometimes their condition is not their fault. There would be nothing to be gained by "re-moralising" society so that the children of divorced couples were stigmatised or fat children made figures of fun.

If we want to encourage more personal responsibility, then it must be of a modern and sensitive kind, that takes into account what we now know about child development, addictive behaviour and the enforcement of social norms.

The question is: what is the role of government intervention? Does it squeeze out personal responsibility or does it support it? That is likely to be the central argument of politics over the next two years. Green taxes could penalise waste and reward responsibility; much of the welfare state and the criminal justice system still needs to be recast along these principles. Mr Brown and Mr Cameron have much further to go. We must admit that we remain unconvinced about the role of Government – or the responsibility of supermarkets – in making people thin.