Smoking and the Law
UK smoking law refers to tobacco, lit tobacco and smoke. You may not smoke in any public place that is enclosed or partially enclosed. These laws do not apply to Vaping because there is no tobacco, nothing is lit and there is no smoke, just an inert water vapour or mist. The exact wording is:
“Smoking” refers to smoking tobacco or anything which contains tobacco, or smoking any other substance; and smoking includes being in possession of lit tobacco or anything lit which contains tobacco, or being in possession of any other lit substance in a form in which it could be smoked.” The Health Act 2006. Chapter 28, Part 1, Para 2
You can easily prove that you are not smoking by Vaping near a Smoke Alarm, directing your exhaled vapour in its direction. The smoke alarm will not activate and sound the alarm because there is no smoke.
Some airlines even sell E-Cigs to passengers in aircraft.