More than 2 million people are thought to use electronic cigarettes in Britain, but almost all are current smokers or ex-smokers who use the devices to stay off tobacco, according to a survey published on Monday.

The anti-tobacco charity Ash (Action on Smoking and Health) says the number of e-cigarette users has tripled from 700,000 in 2012. Nearly two-thirds of users are smokers and the other third are ex-smokers, Ash says, while use of the devices among non-smokers is negligible, at only 0.1%.

Ash's findings are released on the day that a consultation on e-cigarette advertising closes. The Advertising Standards Authority has been examining concerns, particularly among public health doctors, that marketing encourages non-smokers and particularly children to try them, and that they will graduate to ordinary cigarettes.

But Ash's survey, carried out by YouGov, suggests this is not happening and that people are using e-cigarettes to kick their tobacco habit instead.

"The dramatic rise in the use of electronic cigarettes over the past four years suggests that smokers are increasingly turning to these devices to help them cut down or quit smoking. Significantly, usage among non-smokers remains negligible," said Deborah Arnott, Ash's chief executive.

"While it is important to control the advertising of electronic cigarettes to make sure children and non-smokers are not being targeted, there is no evidence from our research that e-cigarettes are acting as a gateway into smoking."

YouGov surveyed more than 12,000 people, with Ash extrapolating the total number of e-cigarette users in the population from the findings.

In a similar YouGov survey in 2010, 8.2% of current or ex-smokers had tried e-cigarettes, but now half of them have (51.7%). In 2010, only 2.7% said they used them on a regular basis, but now that is up to 17.7%.

Among current e-cigarette users, the main reason given by ex-smokers was "to help me stop smoking entirely" (71%) and "to help me keep off tobacco" (48%). The main reason given by current smokers was to "help me reduce the amount of tobacco I smoke, but not stop completely" (48%) followed by "to save money compared with smoking tobacco" (37%).

A study from University College London earlier this month had similar findings. The Smoking Toolkit Study carried out in England found that e-cigarettes were taking over from nicotine gum and patches as an aid to giving up smoking.

The leader of that study, Professor Robert West, said: "Despite claims that use of electronic cigarettes risks renormalising smoking, we found no evidence to support this view. On the contrary, electronic cigarettes may be helping to reduce smoking as more people use them as an aid to quitting."

The consultation is looking at whether advertising rules need to be changed for e-cigarettes. Some public health doctors argue that advertising could normalise ordinary cigarettes, which have otherwise become pariah products.

The e-cigarette industry said the Ash survey showed that public health opponents, such as the British Medical Association, were wrong to oppose the devices as determinedly as they do. "Study after study is showing that scaremongering that e-cigarettes are luring people into tobacco is baseless nonsense. The reverse is going on – smokers are switching into e-cigarettes as the way to reduce the harm from tobacco," said Charles Hamshaw-Thomas, legal and corporate affairs director of E-Lites.