This is a great example of how convoluted and contradictory the rules surrounding the use of e cigs currently are, and the only way to be absolutely certain is to check directly with the airline that you will be flying with. As a general rule no major airline flying from any UK airport will permit the usage of an e cig on board the plane, even though most will happily sell them in their duty free!
As to whether or not you can take one on a plane, be aware of these following pointers:
All UK based security and customs officials will recognize an e cig so won’t have any issue with it being taken on board. The same may not be true when flying from countries where they aren’t in common use – in which case it may be best todefinitelykeep it within your hand luggage so you can explain the device to officials, and avoid the risk of it being confiscated by hold luggage security.
Incidental advice – the vast majority of countries are fine with e cigs, but in a couple they are prohibited. You don’t want to be the first person in history prosecuted for e cig smuggling…
One potential problem could be with taking over 100ml of liquid onto a flight with hand luggage – it’s unlikely to be an issue for all but the heaviest vaper but something to be aware of. The same rules will apply as with any other liquid, namely that it will need to be kept within a clear plastic bag.
Users of lithium ironbattery based e cigs may encounter more problems though as some airlines prohibit such materials being stored within hold luggage. However they will usually allow it to be carried within hand luggage, so again the safe bet is to just check in advance if you do use one of these styles.
So in a nutshell it’s generally fine for 99% of journeys, but if travelling to more exotic climes or using lithium iron batteries just be aware of the potential issues.