London - Switching to e-cigarettes could save millions of smokers' lives, a conference on the rapidly expanding use of the devices heard Tuesday, though some delegates warned more research on the health effects is needed.The merits of e-cigarettes were thrashed out at a one-day gathering of scientists, experts, policy-makers and industry figures at the Royal Society in London.The use of electronic cigarettes - pen-sized battery-powered devices that simulate smoking by heating and vaporising a liquid solution containing nicotine - has grown rapidly.Sales have doubled annually for the last four years and there are an estimated seven million users across Europe.Many delegates merrily "vaped" away throughout the conference sessions, including one man with a luxuriant moustache puffing away on an e-pipe."Cigarettes are killing 5.4 million people per year in the world," said Robert West, a health psychology professor and the director of tobacco studies at Cancer Research UK.He said switching to e-cigarettes could save millions of lives, but the debate was about "whether that goal can be realised and how best to do it".The professor said almost a third of attempts to quit smoking involved e-cigarettes.Doctor Jacques Le Houezec, a consultant in public health and tobacco dependence from France, told delegates that while e-cigarettes contained some harmful substances, the levels of toxicants were nine to 450 times lower than in cigarette smoke.Kodak momentHe said the exponential growth of e-cigarettes was being led by smokers, not scientists.Deborah Arnott, chief executive of the Action on Smoking and Heath (ASH) pressure group, said e-cigarettes could be a leap forward for public health but warned that not enough was known about their effects - and pointed out that the tobacco companies are snapping up the e-cigarette manufacturers."ASH thinks that e-cigarettes have significant potential. They are a lot less harmful than smoking. Clearly smokers find them attractive, primarily as a way of quitting and moving away from smoking, which they know will kill them," she told AFP."But at the moment I think the jury's out and these products need regulating because there's a real concern that their safety and effectiveness is not guaranteed without regulation."The tobacco companies are moving in. For them it's potentially a 'Kodak moment' because if everyone moved to e-cigarettes, they'd lose their market so they've got to be in there. A lot of the bigger e-cigarette companies have already been bought up."She warned: "If there are carcinogens in there, you won't see an immediate effect but 10, 15, 20 years down the line, people will be dying from that."The development of e-cigarettes is definitely running ahead of the science."