The number of people in the UK who have tried e-cigarettes has almost doubled in just two years, according to a new study.
The research, from scientists at Imperial College London, examined e-cigarette use - and attitudes to the devices - across Europe between 2012 and 2014.
The paper, published in the journal Tobacco Control, found that the proportion of people in the UK who had tried an e-cigarette had increased from 8.9 per cent to 15.5 per cent - higher than the European average.
The research also showed the proportion of people across Europe who considered the devices dangerous had also nearly doubled, from 27 per cent to 51 per cent.
E-cigarettes work by delivering nicotine into the lungs in the form of a vapour. The devices contain nicotine in a solution of either propylene glycol or glycerine and water, and sometimes flavourings. When a person sucks on the device, a sensor detects the air flow and heats the liquid inside the cartridge, causing it to evaporate.
Experts fiercely debate whether the devices help people give up smoking, and if they are safe - with some studies raising concerns about the toxicity of some of the ingredients.
Dr Filippos Filippidis, lead author of the research from the School of Public Health at Imperial said: "This research shows e-cigarettes are becoming very popular across Europe - with more than one in ten people in Europe now having tried one of the devices. However there is debate about the risks and benefits associated with e-cigarettes. For instance we don't know whether we may start to see diseases emerge in 10-20 years' time associated with some of the ingredients. We urgently need more research into the devices so that we can answer these questions."
The research, which used data from over 53,000 people across Europe (at least 1000 people from each country), also revealed France had the highest use of e-cigarettes - with one in five people saying they had tried the devices.
The nation also saw the largest rise in the proportion of people who had tried an e-cigarette - nearly tripling from 7.3 per cent in 2012 to 21.3 per cent in 2014.
The average number of people across Europe who had tried an e-cigarette increased by 60 per cent between 2012 and 2014, from 7.2 to 11.6 per cent.
The nation with lowest number of people who had tried an e-cigarette was found to be Portugal, with 5.7 per cent. The reason for the variation between nations is unknown, says Dr Filippidis, though possible reasons include the differences in the number of cigarette smokers, the types of smoking bans that exist in different countries, and also the levels of advertising for the devices.
Most of the people who had tried e-cigarettes were former or current smokers, though the number of people who had never smoked cigarettes, yet had tried e-cigarettes, had also increased from 2012 to 2014.
Dr Filippidis added: "Although this data shows most of the people who use e-cigarettes are current or former smokers - which suggests the devices may be helping some of them quit smoking - it is worrying that some people who have never smoked are using them. This raises the question of whether they could be a 'gateway' to smoking conventional cigarettes."
The research also found that being in the age range 18-24, living in a town or city, and being more highly educated were linked to increased odds of ever having tried an e-cigarette.
The team analysed responses to two Special Eurobarometer for Tobacco surveys carried out in early 2012 and late 2014, on the perceptions and use of e-cigarettes, among a representative sample of adults (15+ years) from 27 EU member states, excluding Croatia.