The doctors' trade union, the British Medical Association, has called for smoking to be banned in cars. Not just cars with children present, but all private vehicles.

Think about that for a minute. It would mean that an adult sitting at the wheel of his own car, alone, could light a cigarette and be stopped by the police.

He might get an on-the-spot fine or find himself in court, given penalty points plus a substantial fine. If he refused to pay the fine, he could go to jail.

The BMA justifies this Orwellian scenario on the grounds that smoking is 'bad' for us.

Potentially, that's true. Few people dispute that there are health risks associated with smoking, some serious. But we know that and as adults it's our choice to smoke, drink, eat fatty foods or go skydiving. How dare the BMA dictate how we live our lives in our own private space?

Nudging, they argue, doesn't work. So the so-called 'caring profession' has decided that the heavy hand of the law must force us to change our behaviour. There's nothing caring about coercive legislation that is simultaneously designed to inconvenience and stigmatise a significant minority of the adult population.

In less than a decade Britain has been transformed from a well-meaning, if intrusive, nanny state to a nasty, coercive bully state, that favours legislation above education and common sense.

Predictably, much of the debate has focused on 'the children'. Legislation, we are told, is needed to protect children from environmental tobacco smoke (ETS).

I don't defend people smoking in a small enclosed space if children are present. It's inconsiderate at least, and where children are concerned it's probably best to err on the side of caution or, as some would say, courtesy.

In reality, however, only a very small minority of smokers still light up if a child is in the car and, contrary to popular belief, peer-reviewed science, taken as a whole, does not support the argument that smoking in cars is a health risk to other passengers, including children.

As for the claim that ETS in a car is "23 times more toxic in a vehicle than in a home" (or a non-defined 'smokey' pub), I want to see evidence of harm, not just a catchy soundbite.

Writing in the Canadian Medical Association Journal last year, Ross MacKenzie of the School of Public Health at Sydney University said: "In [an] exhaustive search of the relevant literature, we failed to locate any scientific source for this comparison."

No surprise there. Tobacco control campaigners routinely play fast and loose with the truth.

Remember those unsubstantiated claims that 11,000 non-smokers died every year in Britain as a result of exposure to so-called secondhand smoke? It was based on estimates and calculations, not hard evidence.

Now they're excelling themselves. A ban on smoking in all cars and, by extension, the home is necessary, they say, because of the cancer-causing particles that smokers allegedly leave on clothes and furnishings, including car seats. Having invented the concept of secondhand smoke to scare us to death, they now want us to believe that 'thirdhand smoke' is a killer too.

Grasping at straws, the BMA would also have us believe that smoking while driving is a serious threat to other road users. The use of mobile phones, they say, is banned while driving, so why not smoking?

One, the use of mobile phones while driving was clearly associated with several fatal accidents where it was proved that drivers had been on the phone at the exact moment of impact. No road accident, to my knowledge, has ever been blamed on a driver smoking or dropping his cigarette while driving.

Two, although the Highway Code lists smoking as a potential distraction while driving, it has not been banned for one very good reason. International studies show that, in the overall scheme of things, smoking is a very minor distraction compared to fellow passengers, unruly children, changing a CD or retuning the radio. Perhaps we should ban them too, just in case.

So why is the BMA calling for a comprehensive ban on smoking while driving? My view, for what it's worth, is that it's tactical. The BMA's declaration coincides with the second reading of Labour MP Alex Cunningham's Private Members' Bill, which calls for a ban on smoking in private vehicles when children are present. It's listed to be debated on Friday 25 November.

The BMA has possibly worked out that by calling for more extreme action, the coalition government may see a ban on smoking in cars with children as a reasonable compromise.

It's not. It's no less illiberal than a complete ban because, for the first time, it would take our laws on smoking into what is clearly private territory. Ban smoking in cars with children on the contentious grounds that their health is at risk and the next logical step is to ban smoking in the home or, at the very least, the kitchen or the sitting room - anywhere, in fact, where a child might stumble today, tomorrow or even next week.

Anti-smoking activists say that's not their objective. But they would say that, wouldn't they?

A decade ago the height of their ambition was more no-smoking areas in pubs and clubs. Within a few years that became a comprehensive ban on smoking in every pub, club and café in the country.

Five years ago campaigners would have denied that a ban on smoking in private vehicles was on the agenda, yet here we are. If government gives in to the fanatical and puritanical anti-smoking industry, do you really think they won't be demanding a ban on smoking in our own homes?

Hopefully common sense will prevail and the government will have the sense to butt out. It's not much to ask.