Electronic cigarettes are not all that harmless. While smoking them one inhales a fine heated mist.

The cigarettes use replaceable cartridges with shots of nicotine and have become popular because they are not covered by the smoking ban.

Companies are marketing the electronic cigarettes as a way of getting round the ban.

And in recent months they have reported a rise in sales with some selling over 1,000 of the £40 starter-packs a month.

While the products do not contain tar, tobacco or carbon monoxide, experts are worried as users inhale a fine heated mist and there is a lack of regulation.

But retailers said they were healthier than normal cigarettes.

However, campaigners including the World Health Organisation, have raised concerns, pointing out there was a lack of knowledge about the products.

Douglas Bettcher, of the World Health Organisation, said there was a "regulatory blackhole" which meant no-one knew just what these products contain.

"We are facing a new product. We do not know what is in these cartridges besides nicotine. What are the effects of heating and vapourising the nicotine and inhaling it?"

And Deborah Arnott, of anti-smoking group Ash, pointed out that many of the products were made in China where quality control was "not very good".

"I think our concern is that we would really like smokers to use safer nicotine products but there is a regulatory gap.