E-cigarettes deliver a nicotine hit in vapour form. Fans say they are safer than regular cigarettes and shouldn't face the same regulations and advertising restrictions. The UK's Faculty of Public Health says it doesn't know yet whether e-cigarettes do more good than harm. And the World Health Organisation is due to give guidance to governments later this year.

Now, a group of 53 scientists has published an open letter calling on the WHO to "resist the urge to control and suppress e-cigarettes". So, who is right? Should e-cigarettes be classed as tobacco products and face the same restrictions as cigarettes? Or should they be welcomed as effective aids to giving up smoking, and be prescribed free on the NHS?

They do seem to work. E-cigarettes heat liquid nicotine to a vapour, which is inhaled. Realistic touches like a light in the tip and water vapour "smoke" make them look and feel like a regular cigarette. They deliver the nicotine rush that smokers are addicted to, without the tar and chemicals that can cause cancer and disease.

A large survey of smokers in England conducted by University College London (UCL) found that one in five of those who are trying to quit manage to do so while using e-cigarettes. Of course, that suggests that four out of five don't manage to quit. But nicotine is a highly addictive drug and giving it up is notoriously hard. This quit rate is still 60% higher than if people try to quit without any professional input, even if they buy nicotine products over the counter. Smokers who go it alone hardly ever manage to quit. And proponents say that as the devices get more sophisticated, with different strengths and flavours of nicotine, more people may switch from regular cigarettes.

So e-cigarettes can help smokers to give up, but they are not as good as pitching up at an NHS stop-smoking service, according to Professor Robert West, director of tobacco studies at UCL, lead author of the study and a signatory to the open letter. He says these services "almost triple a smoker's odds of successfully quitting compared to going it alone or relying on over-the-counter products".

Professor West has said that banning the sale of e-cigarettes to under-18s is a sensible precaution to prevent adolescents starting with e-cigarettes and then going on to tobacco. And the BMA has also expressed concern about children taking up smoking after being introduced to e-cigarettes .

There is nothing to stop you puffing on an e-cigarette in a restaurant or public place. The nicotine vapour is odourless and it would be hard for fellow diners to complain. In reality, you may feel a bit of a prat as non-smokers look on disapprovingly and "real" smokers acknowledge their pariah status by going outside.

Critics of e-cigarettes say they may be less risky than regular cigarettes, but we can't say that they're harmless. The devices can be unreliable and of variable quality. Their growing popularity is undoing decades of hard work trying to persuade people that smoking isn't cool and can kill you. Kids and non-smokers may be tempted to take up smoking as a result of positive media images.

But experts such as the 53 signatories of the open letter feel that e-cigarettes are a valuable way to reduce the terrible burden of smoking-related disease. It's true that rates of smoking have fallen from 40% in the 1970s to 20% now. But that's still 10 million smokers in the UK, of whom half will die of a smoking-related disease an average of 10 years younger than non-smokers.

And the worry about kids or non-smokers taking up smoking after trying an e-cigarette seems misplaced at the moment. 99% of people who use e-cigarettes in the UK are ex or current smokers and very few are kids. Smokers who are trying to quit prefer e-cigarettes to other nicotine-replacement therapies, even though they're not licensed and can't be prescribed.

E-cigarettes may help some, but realistically once you are a smoker the odds are against you ever quitting. The holy grail is to stop people from starting to smoke. Smoking must be portrayed as deeply uncool; smokers must remain huddled in doorways and not let back inside; and public health messages must be clear and unambiguous. The professionals' bickering about e-cigarettes will confuse the public and muddy the waters. Time for them to smoke the peace pipe.