London researchers have dismissed recent health warnings over e-cigarettes as "misleading," saying they have the potential to save tens of thousands of smokers every year.

For every million British smokers who give up tobacco products in favour of e-cigarettes, more than 6,000 premature deaths could be prevented annually, experts from University College London (UCL) have said.

They estimated that would equal over 54,000 lives saved every year, were all of Britain's nine million smokers to switch.

The findings come in stark contrast to recent warnings over potential health risks associated with electronic cigarettes.

The World Health Organisation (WHO) has warned that bystanders can inhale significant levels of toxins from the vapour, and that they could be acting as a gateway to tobacco smoking.

But according to Professor Robert West and Dr Jamie Brown from UCL's Department of Epidemiology and Public Health, the concentration of toxins in e-cigarettes is in fact "very low".

In an editorial published in the British Journal of General Practice, they argued that the vapour contains "nothing like the concentrations of carcinogens and toxins as cigarette smoke".

"In fact, toxin concentrations are almost all well below one twentieth that of cigarette smoke."

Nevertheless, their figures accounted for the possibility that the devices carry an increased risk of death.

Their findings coincided with a separate report published by researchers from Kings College London who slammed WHO's findings as "misleading".

Last week WHO called for stiff regulation of the devices and a ban on indoor use. It also suggested restrictions on advertising and on sales to minors.