IT is the latest accessory for smokers wanting to quit: the green, glowing e-cigarette.

However, with the number of users expected to reach one million by the end of 2013, the debate over the use of the products is becoming ever more heated.

A leading Scottish researcher has called for more stringent controls to prevent "dangerous" claims e-cigarettes – which contain nicotine – can help smokers quit tobacco. Professor Gerard Hastings, of Stirling University's Centre for Tobacco Control Research, said there is a lack of evidence e-cigarettes actually work.

The e-cigarette industry, meanwhile, has launched a battle against moves to regulate the products as medicine, claiming it will cost the NHS billions of pounds by leading to a drop in smokers using them to quit. But one of the UK's leading brands of e-cigarettes has insisted they are "absolutely not" being marketed as an aid to stopping smoking.

E-cigarettes, which debuted in 2004, are battery-powered devices that let users inhale nicotine vapours, but don't contain harmful tar and carbon monoxide found in tobacco smoke.

Hastings recently published a study commissioned by Cancer Research UK on nicotine-containing products. The study noted that health watchdog body, the National Institute for Clinical Excellence, said while little is known about the safety of e-cigarettes at present, they are likely to be less harmful than cigarettes.

But Hastings said allowing unproven claims about their ability to help smokers quit was "really dangerous".

"The great risk is people start to think about these things like they are a silver bullet, and then it doesn't work," he said. "They are at best disappointed – at worst they are completely demotivated and think, 'I can't give up'. It is a phoney promise if they aren't very helpful in aiding people to stop smoking – and we don't know whether they are or not.

"There are good reasons why we regulate medicines and insist that pharmaceutical companies only make claims they can prove."

He added: "I would very much like to see much, much more rigorous control on the marketing. People should not be making claims for these products that are not proven.

"The point is that if you introduce a new device onto the market, you should be able to prove it is effective. None of these e-cigarettes are of proven effectiveness."

Hastings said he also had concerns about the marketing of the products as an alternative to cigarettes in situations where smoking is not allowed. "In other words, it is a means of overcoming the inconvenience of smoke-free legislation," he added.

"One of the sub-plots of smoke-free legislation was it did make smoking more difficult and therefore made people think, 'Maybe I will give up'."

The Medicine and Healthcare Products Regulatory Agency (MHRA) announced in June that the Government is to regulate e-cigarettes as a medicinal product. The restrictions will come into effect in 2016.

In some countries, including Austria, Estonia, Romania and Sweden, they are already treated as medicinal products; in others including Brazil, Norway and Singapore, the sale of e-cigarettes is banned.

Last week, a round-table discussion was held at the House of Lords involving the MHRA and representatives from e-cigarette brand, E-Lites.

A briefing produced by E-Lites ahead of the event claimed the MHRA stance on regulation of e-cigarettes is leading to most pharmacies currently declining to stock them.

It forecast this will mean 390,000 fewer people using e-cigarettes in the UK, with an annual cost to the NHS of people failing to quit smoking of £2.51 billion a year. It also referenced an Italian study published this year which found that 8.7% of e-cigarette users successfully quit smoking.

However, Charles Hamshaw-Thomas, director of legal and corporate affairs at E-Lites, told the Sunday Herald it was "absolutely not" marketing the products as a smoking cessation aid.

"The MHRA thinks we are competing with the pharmaceutical drugs and nicotine-replacement products," he said. "Absolutely not. We are competing as an alternative to cigarettes."

He added: "It is clear they are having a high level of usage by people who are trying to stop or reduce their smoking of tobacco and that is the reason why they are incredibly successful – a lot of people want to reduce their tobacco consumption.

"We think it is a slightly unfortunate situation at the moment, in that we have a lot of consumers saying they have been tremendously helpful in reducing their use of tobacco.

"But as soon as we repeat those [comments] we get asked by the MHRA to desist - because by repeating what our consumers say we are making a medicinal claim."

Hamshaw-Thomas said he was "very surprised" at the idea e-cigarettes might undermine anti-smoking legislation by taking away the difficulty in getting a nicotine-hit.

"Shouldn't we be all rejoicing in the reduced level of tobacco consumption?," he said. "It doesn't smell, it doesn't provide the awful odour and litter, so why aren't we celebrating this instead of finding reasons to criticise it?"

Sheila Duffy, chief executive of anti-tobacco charity ASH Scotland, said e-cigarettes had a role to play in helping smokers but welcomed their regulation. She added: "However, we are concerned at the long lead-in time before implementing regulation for e-cigarettes. What will happen over the intervening three years to ensure the quality and consistency of the devices and tackle the capacity for promotion to children and other new markets, which are already a worry?"