First they came for them on planes and trains.

Then they moved on to the workplace. A few years later they targeted shops, restaurants and pubs. Even bus shelters were beyond the pale. Gradually, all but the thickest-skinned smokers got the message. Their fags were not welcome. Braving sleet and gales, they huddled outside cafes and offices, risking pneumonia for the sake of a drag. But it was only going to get worse, and in their bones they knew it.

The recent Commons vote to ban smoking in cars carrying children represents a more aggressive and invasive approach to protecting people from the effects of passive smoking. And very malign they are too. Those adverts showing a child in the back seat with a noose of smoke around its neck may have been emotive, but they were also alarmingly accurate.

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By now, smokers must feel there's nowhere safe left for them to go but home. How naive. If new information is acted upon by Holyrood, the tobacco fraternity will soon have to head for the hills if they want to light up in peace. Following a report by Ivy Shiue, an environmental health expert at Heriot-Watt University, even enjoying a cigarette in their own kitchen could be under threat.

Dr Shiue's statistics reveal how much harm passive smoking in the home does to children. The figures are as eye-watering as an unfiltered Gauloise. Based on a study of thousands of Scottish families, she demonstrates that passive smoking is strongly linked to strokes, angina and heart attacks. It also affects children's sleep, concentration and confidence. Across the UK, she reports, children's exposure to smoke results in 10,000 hospital admissions a year. In the wake of her findings, lobby groups are urging the Scottish Government to ban smoking in family homes.

Even now I see steam issuing from ears as well as nostrils. And in some cases, one sympathises. More aware than ever before about the effect of smoke on others, many parents already banish themselves to the doorstep. Years ago a friend of mine used to frogmarch her chain-smoking father-in-law to the greenhouse rather than have him pollute her children's lungs, as he had her husband's, whose chronic asthma she attributed to a childhood spent under a cloud. At the time I thought she was a bit harsh; now I see she was at the medical cutting edge.

Yet if the state begins to police what people do in private, however worthy the cause, where does such interference end, and what sort of vigilante society will we have created? It is one thing for foster charities to urge that under-fives are not placed with smokers, and to offer those taking in older children help to quit or "to establish a smoke-free home", as the Fostering Network's website puts it. In such cases, the authorities have a duty to take the utmost care of their charges.

That they deem such safeguards necessary reinforces the fact that smoking hurts the young. But isn't a diet of junk food potentially as damaging? With national levels of child obesity rising fast, the long-term impact of poor nutrition and over-eating on children's health is potentially as damaging as that of second-hand tobacco. So even if, as one hopes, the fight against passive smoking is eventually won, will the government then come under pressure to ban sugary drinks from family fridges, or to put surveillance cameras on wheelie bins for evidence of excessive consumption of cheese burgers and chocolate?

While a ban on smoking in cars with children is long-overdue, when it comes to the home, the best way to change people's behaviour is not by handing out warnings and fines. As with the smacking ban, policing what goes on behind the front door is all but impossible. Winning hearts and minds rather than putting up backs is essential since, in the end, one has to trust individuals to do the right thing. That, in turn, will only happen if people are well-informed and make a willing choice.

Education, not humiliation, is the way to a healthier country. It will take hard-hitting anti-smoking campaigns, not a bobby at the door, to change attitudes. Otherwise, like outlaws of old, those who cannot give up tobacco will start to feel they are being smoked out of their homes, metaphorically as well as literally.