As a breed, Conservative politicians hate the nanny state. So do right-wing columnists, some of whom are still whining about the fact that they can't smoke in public places.

Any suggestion that the principles behind the smoking ban be extended to junk food prompts near-apoplexy, as though we have an inalienable right to consume as much high-fat, sugary rubbish as we wish.

I've never been convinced that eating popcorn is a human right, and the argument that governments shouldn't intervene in the nation's eating habits looks shakier than ever. According to an analysis carried out at the Wolfson Institute of Preventive Medicine and published last week, around 40 per cent of cancers could be avoided by a change in lifestyle. High among the bad habits that need to be tackled are smoking and excess body weight, which we've known for a long time, but the study makes hard-hitting claims about the specifics.

Among women, being overweight ranks second (after smoking) in the lifestyle factors linked to cancer, while for men it is fifth. The analysis suggests that 17,000 cancers a year are linked to excess weight, but warns the figure may be an underestimate. Another 29,000 may be attributable to poor eating habits, from insufficient fruit and vegetables to excess red meat and salt. Overall, the analysis suggests that around 134,000 cases of cancer a year are linked to environment and the way people live, including poor diet, weight, smoking, alcohol consumption and inactivity.

That figure is bound to rise as more people exceed sensible weight limits, with one study published in The Lancet predicting that half the population could be obese by 2030. The cost in extra health care alone would be about £2bn a year, and that's without taking into account all the misery caused by cancer and other obesity-related conditions such as heart disease. Last week, cancer charities were keen not to blame individuals for habits that raise their risk; it's clear that many people find it hard to resist fatty food and cheap alcohol, which leaves government intervention the only serious option.

It's worked with smoking, which used to be enjoyed by more than half the male population and has now dropped to a fifth. The success of campaigns against tobacco, from graphic health warnings on cigarette packets to high rates of tax and an advertising ban, provides an optimistic model of how self-destructive behaviour can be altered. But Labour governments were never as bold about tackling the food and drinks industry, and Conservative politicians have a visceral loathing of imposing punitive rates of tax on, for example, cheap alcohol and fatty food.

Of course they don't have the same scruples when it comes to other species of "interference" in people's lives, such as telling them they shouldn't expect to depend on state benefits. Cancer charities claimed last week that new proposals mean even patients on chemotherapy in hospitals will have to prove they are too sick to work. The Government says the proposals have been misunderstood, but wouldn't it be more sensible to try to reduce the number getting cancer in the first place?

Thousands of lives have been saved by the smoking ban. Unless it wants to look criminally irresponsible, the Government should tackle weight and alcohol problems with the same ferocity. Bring on the nanny state, and ignore the predictable protests.

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