Imagine the look on Gordon Brown's face when he saw the results of Bupa's poll this week suggesting that 34% of the British public think that those who smoke, drink or are obese should take the rap for their self-inflicted bad health by being charged for their medical treatment.

That would certainly go some way to relieving the financial burden that these unnecessary health problems impose on the NHS. And it's a hefty sum, running to an estimated £6bn per year in the case of poor diet and £1.7bn for smoking-related diseases. That's the kind of saving that would put a smile on any chancellor's face.

And why not penalise people for their behaviour? It's not as if they don't know what they're doing to themselves. There can't be a single person who isn't aware that smoking, or eating high-fat foods are bad for you. And anyone who saw the photos of George Best at the weekend should be under no illusions about the evils of drink.

And that's not all. This week the Lancet published the results of a worldwide study showing that one third of all cancers could be prevented if people would kick these bad habits.

So why should those of us who try to look after ourselves be forced to pay for the hospital care of those who blatantly don't? It's a free world and that's their right, but surely with rights come responsibilities.

But is there evidence that financial penalties such as those suggested in Bupa's poll make a difference to people's behaviour? Yes, according to Treasury figures, which show that every 10% increase in the price of cigarettes leads to a 4% drop in smoking and a similar price increase for alcohol leads to a 10% fall in consumption.

Although there are obvious merits to this approach, it is far too simplistic. Blanket taxation makes no allowance for individual factors, such as the protection a person may get from their genes. For whatever reason, some people can smoke 40 cigarettes a day for 80 years with no ill effect.

So is the answer to charge individuals every time they visit a doctor or a hospital? Aside from the fact that it would go against the whole ethos of the NHS, there's a real fear that given the demographics of these conditions, this would be unfairly punitive to those who are already the poorest in our society.

And what would happen if they couldn't pay? Would they be thrown in jail or simply be refused treatment? Or perhaps - more likely - they simply wouldn't seek medical attention and we would end up with a two-tier health system such as that in the United States where the most needy are excluded from the best care.

Luckily, charging isn't the only option. Public health researchers advocate much broader strategies of general health promotion. These include the bans on tobacco advertising along with media campaigns such as the current one by the British Heart Foundation which graphically warns of the dangers lurking in fast foods.

Then there are the strategies that have direct impact on individuals themselves, such as banning smoking in public places, better health education in schools, promotion of NHS-funded nicotine replacement therapy for smokers and Slimming World vouchers for the overweight.

It's estimated that for smoking alone, these measures could lead to 29 million smokers quitting and avert six million deaths worldwide. Not to mention massive financial savings.

But the main message from the Bupa poll is that as a society we believe that those whose lifestyle puts them at increased risk of disease should be more accountable for their actions and the resultant financial strain they put on the healthcare system should not be shared with the rest of us.

Because while at present it's free for everyone at the point of access, that freedom should not be taken for granted. One day - the day they need it most - it may not be there for them

· To ask Simon a question, email health@theguardian.com. Please note he cannot enter into any correspondence.