Video report by ITV News Science Correspondent Alok Jha.
E-cigarettes are much less harmful to health than smoking, a new report has concluded.
The Royal College of Physicians (RCP) report says that e-cigarettes should be widely promoted as a substitute to smoking.
Experts at the College looked into the science, public policy, regulation and ethics surrounding e-cigarettes and made a series of conclusions about the devices including:
E-cigarettes are not a "gateway to smoking" - in the UK, use of e-cigarettes are used mostly by those who are already using, or have used, tobacco, they said.
There is no evidence that e-cigarettes result in normalisation of smoking.
The devices are beneficial in encouraging smokers to quit.
There is a possibility that the devices may result in some long-term harm because of the inhalation of the ingredients other than nicotine - but the harm that could be caused is substantially smaller than that caused by smoking, the authors said.
While there is a need for "sensible" regulation of the devices, regulation should not significantly inhibit the development and use of the products, they add.
Professor John Britton, chair of the RCP's Tobacco Advisory Group, said: "The growing use of electronic cigarettes as a substitute for tobacco smoking has been a topic of great controversy, with much speculation over their potential risks and benefits.
"This report lays to rest almost all of the concerns over these products, and concludes that, with sensible regulation, electronic cigarettes have the potential to make a major contribution towards preventing the premature death, disease and social inequalities in health that smoking currently causes in the UK. Smokers should be reassured that these products can help them quit all tobacco use forever."
Duncan Selbie, chief executive at Public Health England, added: "The evidence is clear; vaping is much less harmful to health than smoking, and this report further highlights the important role of e-cigarettes in reducing the deadly harms smoking causes.
"The best thing a smoker can do, for themselves and those around them, is to quit completely, now and forever. E-cigarettes are the most popular quitting aid in England and local stop smoking services are the most effective route to giving up, we encourage smokers to combine these, giving them an extremely good chance of quitting smoking successfully."