Image copyright Getty Images Image caption The UK smoking ban does not apply to e-cigarettes

Under-18s in England are to be banned from buying electronic cigarettes, the government has announced.

Experts say it is not yet known what harm the tobacco-free devices could inflict and that their contents could be damaging young people's health.

An estimated 1.3m people in the UK use e-cigarettes which were designed to help smokers quit.

Ministers also plan to make it illegal for adults to buy traditional cigarettes for anyone under 18.

Analysis Electronic cigarettes mimic the effects of real cigarettes, producing a vapour that is potentially less harmful than cigarette smoke and free of some of its damaging substances, such as tar. The vapour does often, however, contain nicotine, the addictive substance that provides the "hit" in cigarette smoke. The jury is still out about just how safe e-cigarettes are, and nobody knows what their long-term impact is on health. There are plans to licence e-cigarettes as an aid to quitting smoking from 2016, but at present they are not available on the NHS, unlike other smoking cessation aids such as nicotine patches. Because they are not regulated, the contents of e-cigarettes can vary. Some have been found to contain toxic chemicals which are also found in tobacco, and have been linked to cancer. There is also only sketchy evidence that e-cigarettes help people to give up smoking.

While smoking rates have fallen to their lowest ever level, experts fear the electronic substitutes could be encouraging teenagers to take up the habit.

The battery-powered devices, which can be bought online and in some pubs, chemists and newsagents, deliver a hit of addictive nicotine and emit water vapour to mimic the feeling and look of smoking.

The vapour is considered potentially less harmful than cigarette smoke and is free of some its damaging substances such as tar.

Image copyright PA They could be extremely damaging to young people's health Prof Dame Sally Davies, Chief medical officer, England

"We do not yet know the harm that e-cigarettes can cause to adults, let alone to children, but we do know they are not risk free," Prof Dame Sally Davies, England's chief medical officer, said.

"E-cigarettes can produce toxic chemicals and the amount of nicotine and other chemical constituents and contaminants, including vaporised flavourings, varies between products - meaning they could be extremely damaging to young people's health."

Katherine Devlin, president of the Electronic Cigarette Industry Trade Association, welcomed the changes in the law, saying they had been asking for it "for years".

"It's high time that it was mandated in law so that it can be robustly enforced," she added, pointing out that product labelling made it clear e-cigarettes were not for under-18s.

Anti-smoking charity Ash also welcomed the changes, but chief executive Deborah Arnott called for a retail licensing system that would mean cigarettes could be legally sold only in shops, not in car boot sales or markets.

No EU ban

The UK currently has few restrictions on the use of e-cigarettes, despite moves in some countries to ban them.

Restrictions have recently been mooted in Scotland and Wales, where health policy is a devolved issue.

A Welsh government spokesman said on Sunday it "fully" supported a ban on e-cigarettes for under-18s and was considering how such legislation could be introduced in Wales.

In Northern Ireland, the NI Chest Heart and Stroke charity is pressing the health minister to introduce a similar ban.

The law change for England will be introduced in Parliament this week as an amendment to the Children and Families Bill.

Labour said the policy on banning cigarettes for children was a "watered-down version of a policy that Labour called for last year" and that buying cigarettes for children should carry the same penalty as buying alcohol for underage drinkers.

But it said restricting the sale of e-cigarettes to under-18s was a "sensible step".

From 2016, the Medicines and Healthcare Products Regulatory Agency is expected to license e-cigarettes as a medicine in the UK.

This will bring them in line with nicotine patches and gum, and allow the agency to apply rules around, for example, the purity of the nicotine in e-cigarettes.

MEPs have rejected calls for a blanket ban on the sale of e-cigarettes across the EU.

However, under a compromise deal, strict limits will be placed on the amount of nicotine they contain, and individual EU member states will be able to introduce a national ban if they see fit.

If three or more member states chose that path, it could trigger an EU-wide ban.

'Irresponsible adults'

Smoking remains one of the biggest causes of death and illness in the UK, with around 100,000 people dying each year from illnesses linked to the habit.

Experts want to crack down on the number of young people smoking by bringing the law in line with restrictions on the sale of alcohol.

The new rules on adults buying cigarettes for under-18s could be in force by the autumn and may mean anyone caught buying cigarettes for a child could be given a £50 fixed penalty notice or a fine of up to £2,500.

"We must do all we can to help children lead a healthy life," public health minister Jane Ellison said.

Some 41% of 15-year-olds who smoke say they usually buy their cigarettes from someone else, rather than from a shop, according to Department of Health figures.