E-cigarettes should be available on the NHS, health officials have argued.

Public Health England (PHE) said patients should be allowed to vape in private rooms and purchase e-cigarette devices in hospital shops to help stop them smoking regular cigarettes.

PHE is also calling for the government to license e-cigarettes as medical quitting aids so that GPs can prescribe the devices to patients trying to stop smoking.

The recommendations come after experts from King's College London, the UK Centre for Tobacco and Alcohol Studies, the University of Stirling and Cancer Research UK concluded that vaping only poses a fraction of the risk of smoking.

PHE experts, writing in The Lancet, said: "Although not without risk, the overall risk of harm is estimated at less than 5% of that from smoking tobacco; the risk of cancer has been calculated to be less than 1%.

"There are two parts to being a smoke-free hospital, one is not allowing smoking on the premises, the other is helping every smoker to quit.

"Some hospitals will decide, especially with their longer-term patients or patients who don't have a choice whether they are there or not, where it will be appropriate to have spaces indoors to have spaces where vaping is permitted.

"The strongest case for that is psychiatric hospitals because [these patients] have got the highest prevalence of smoking and the highest levels of smoking related harm.

"Single occupancy rooms are quite common in mental health trusts so that makes it very easy for people to vape in a single occupancy room without any annoyance to anybody else."

Professor John Newton, director for health improvement at PHE, said: "Every minute someone is admitted to hospital from smoking, with around 79,000 deaths a year in England alone.

"Our new review reinforces the finding that vaping is a fraction of the risk of smoking, at least 95% less harmful, and of negligible risk to bystanders."