Tough new EU rules could see the majority of e-cigarettes forced off the market, in a move which could have dramatic consequences for public health.
A provisional deal between MEPs and national governments could prompt a ban on refillable e-cigarettes and force manufacturers to rely on single-use low-nicotine alternatives.
"This is a perverse decision that risks sending more people back to real, more harmful, cigarettes," European Conservatives and Reformists Group leader and shadow rapporteur on the directive Martin Callanan said.
"Refillable e-cigarettes would almost certainly be banned, and only the weakest products will be generally available. As many smokers begin on stronger e-cigs and gradually reduce their dosage, making stronger e-cigs harder to come across will encourage smokers to stay on tobacco."
The deal, which has not been finalised, could see all e-cigarettes with over 20 milligrams of nicotine brought under new restrictions.
The European parliament is understood to be content with the use of refillable nicotine cartridges, but member states such as Britain and Germany are concerned that the cartridges can contain up to 10 milligrams of nicotine – the equivalent of a carton of 200 cigarettes.
If refillable e-cigarettes are prohibited in at least three member states, the commission would be able to extend the ban to all member states.
If the talks fail, e-cigarettes would remain unregulated, providing a sigh of relief to an industry which could outperform the £700 billion cigarette market within ten years.
Proposals for all electronic cigarettes to be controlled by pharmaceutical legislation were rejected by MEPs.
Liberal Democrat MEP and health spokeswoman in the European parliament Rebecca Taylor said: "Significant ground had been won in the rejection of Europe wide medicines licensing. But the decision to potentially ban refillable cartridges and devices in future would be a backward step."
Euromonitor currently puts the value of the market at £2 billion, but a surge of investment from big tobacco firms like Philip Morris owner Altria, British American Tobacco and Imperial Tobacco show there is widespread belief that electronic smoking could offer a popular substitute to the real thing.
A study published in the Lancet this year showed shifting to e-cigarettes makes smokers at least as likely to quit as using nicotine patches and other research projects also suggest a significantly higher success rate than more traditional nicotine replacement options, like gum.
There are concerns around the safety of the product, however. A study presented at the American Society of Cell Biology in New Orleans showed prolonged exposure to nicotine, either through normal smoking or by e-cigarettes, may damage the heart.