The rules governing personal conduct on the top deck of a Glasgow bus are known to international peacekeeping forces everywhere: keep your head down; do not make eye contact and on no account attempt to make polite conversation with strangers. Refrain, too, from making jerky or unpredictable movements.

It was probably the last of these that I transgressed last Thursday evening as I fished out my electronic cigarette and started puffing. Yet only for a few seconds did subsequent events threaten to get out of hand.

To inhale a good lungful of the nicotine essence that these little missiles produce, it's necessary to suck really hard so that the blue tip glows iridescent and bright. In this way you can sustain the merest hint of a hit at the back of the throat before exhaling enough vapour to make it look as though it's a real cigarette you're smoking. There had been a few tetchy glances from other passengers, especially from a nervy young woman who may, very possibly, have simply wanted to light up herself. Now there's a tap on my shoulder. An older gent with a no-hostages haircut leans forward. "Are you just smokin' that for effect, my friend?" he inquires, pronouncing "friend" as "freen".

"As a matter of fact … yes," say I.

"Well, in that case I think I'll join ye," he says, producing one of his own, which glows green.

It strikes me that if enough of us were to do this in a darkened bus at night-time it might look like a mobile installation. Perhaps we could secure a grant …

For a few days only I had joined the one and a half million or so other Britons who have recently begun to smoke electronic cigarettes. The manufacturers claim these are harmless substitutes for real cigarettes and, as such, could save thousands of lives each year.

It's a claim impossible to verify, but highly unlikely. My single white stick cost £6.99 and is equivalent to 40 cigarettes, according to its makers, a saving of more than 50% on two packets of the real thing. If the recent rate of uptake were to continue, the debate about e-cigarettes' safety would intensify.

On the face of it, they ought to be the elixir of life for cancer specialists and anti-smoking campaigners. Even though they have not been around long enough for a study of other potential harmful effects, it's generally accepted by medics – and reluctantly so by the anti-smoking lobby – that they are less harmful than cigarettes. The devices are powered by battery and deliver nicotine that becomes vaporised before forming an aerosol mist. In some English pubs, groups of users, who like to be known as "vapers", have begun to gather.

At another level, though, e-cigarettes could be seen as insidious wee varmints that insinuate themselves into polite company and corrupt by stealth. As they contain no tobacco and are not actually lit, they can be used legally in those public places where real smoking is illegal. Organisations including Virgin Trains and the Wetherspoons leisure chain are not convinced and have banned them.

Sarti's Italian restaurant in Glasgow city centre was once filled with shoppers and office workers who went to eat pizza, drink coffee and smoke their little heads right off. Since Scotland introduced a smoking ban in 2006, it's been one of those places where it's hard to imagine we were ever allowed to smoke at all. On Thursday lunchtime, among older ladies with hats and elegant dresses and families soon to be parted by university, I fired up the electronic snout and checked discreetly for signs of agitation. As the Observer photographer snapped away, one of my lunching ladies simply had to say something. "Are you modelling those gas cigarettes?" she asked. "Yes," said the passing waiter, "it's for the cover of next month's Vogue." He said it with a snort.

Earlier that day Celtic FC, one of Britain's foremost sporting institutions, had announced it would be supplying another leading brand of electronic cigarettes at outlets within its stadium. It's been the e-cigarette industry's biggest endorsement to date.

Stewart Maxwell, the Scottish Nationalist MSP who championed the smoking ban in Scotland, could barely contain his fury. "I'm very disappointed that a big and successful football club such as Celtic would get involved with this," he said. "The campaign to ban smoking in public places was about de-normalising smoking as an activity in public. This goes exactly in the opposite direction."

I ought to point out here that Maxwell, like Sir Robert Peel, has a smile that resembles the brass nameplate on a coffin lid. Not only is it sinful to smoke, he seems to be saying, it is sinful even to think about it. The nation's first thought crime is surely not very far away now. It is hard to fathom the source of Maxwell's angst. As MSP for the West of Scotland, he will be fully aware how many of his constituents die from smoking-related cancer every year. Even Ash Scotland accepts that e-cigarettes are much safer than tobacco, while remaining concerned that tobacco companies promote dual use of artificial products and real ones.

It's expected that from 2016 the e-cigarette market will be regulated, when the devices are licensed for medicinal use in helping to stop smoking. This should also address fears that unregulated, pirate products could threaten human health. By then, too, a clearer picture will have emerged on whether e-cigarettes are essentially good for those of us who want to quit smoking or whether they are harmful.

Friday evening at Glasgow's Central Station would sort out the men from the boys in terms of attitudes to using these devices in public places. The platforms are teeming with Scotland and Belgium supporters en route to the World Cup qualifier at Hampden later that night. Police and stewards are out in force and I am insouciantly trying to wrap myself in ribbons of white vapour. Soon a couple of big coppers trudge by and then, almost imperceptibly, they slow. They are looking, but pretending not to, and I know why. They don't want to collar someone for a banned activity in a public place only for the smart-arse to brandish his pesky device in their faces. They are on their way again.

After three days of smoking e-cigarettes, I'm not enchanted. I'd only want to use them in those places where I was previously accustomed to smoking: pubs and cafes. And I'd be reluctant to strike them up in places where there are children. I could see them work in hospitals, especially as a late treat for smokers whose lights are about to go out.

Celtic and their new e-cigarette sponsors are kidding themselves if they think their partnership will lead to an outbreak of responsible smoking among supporters. Already I'm told of a workshop in the city going into surreptitious production hollowing out these babies and fitting them with special filters so that real tobacco can be smoked.

On a wild Champions League night, who will be able to tell the difference – or dare to?