More research is needed into the long-term impact of e-cigarettes, a senior health official has said.

The devices are marketed as "interested, exciting and edgy" products, that "that might encourage people to use them in the longer term", according to Professor Gillian Leng, the deputy chief executive at the National Institute for Health and Care Excellence.

Speaking at a meeting of the Science and Technology parliamentary committee, Prof Leng said the long-term impact of using e-cigarettes is not yet known because they are still relatively new.

When asked about the assertion that getting people on to e-cigarettes may maintain an addiction to nicotine, she said: "I think that is the distinction between using e-cigarettes as a quitting aid, which you clearly can do, you downgrade the amount of nicotine you get through the product and it can help you to stop your nicotine addiction.

"The question is whether it becomes a long-term lifestyle choice and I think that there might be questions about that because of the way e-cigarettes are being marketed.

"They are being marketed as an interesting, exciting, edgy product that might encourage people to use them in the longer term."

She added: "We know they are substantially safer than cigarettes

"The risk is that we don't know what the long-term impact of using e-cigarettes is because they are new products and we really need to gather that information.

"They are 95% safer than cigarettes but there is 5% that we don't know about."

But Professor John Newton, director of health improvement at Public Health England (PHE), said there were "reassuring patterns" of e-cigarette use.

He said: "The large scale surveys suggest that there is a progression from being a smoker, to using e-cigarettes, to stopping."

A recent academic review of the devices, published by PHE, concluded that vaping poses only a "small fraction" of the risks of smoking.

It found that e-cigarettes could be contributing to at least 20,000 people quitting smoking every year.

But the review found that two in five smokers had never even tried vaping, PHE said that "many thousands of smokers incorrectly believe that vaping is as harmful as smoking".

Meanwhile England's public health minister has said that he should not "be a cheerleader" for e-cigarettes.

Health minister Steve Brine told MPs: "I get criticised for not being a cheerleader for e-cigarettes.

"I do not think it is my job to be a cheerleader for a sector of industry necessarily.

"I think that our pragmatic evidence base, keeping it constantly under review, puts us in rather a sensible middle."

Meanwhile, the Committee has collated data from mental health trusts and found that a third had banned e-cigarettes.