You show me where the CAA have regulated that e-fags are forbidden in airports and aircraft
It can be nothing to do with them
and rules set by the airline itself.
It is their (the airlines) aircraft and they are free to set their own rules.
It seems some folk would only be content if airlines were to publish all their internal procedures, no doubt so they can pick holes in them.
Looking at a national carrier at random: -
In section IX of their T&C's
1. The Carrier reserves the right to assess, in a reasonable manner, the behaviour of Passengers on board the aircraft, and to estimate according to the circumstances whether said behaviour is likely to obstruct, threaten, or endanger one or more persons, items of property or the aircraft. Passengers must not obstruct the crew from performing their duties and must comply with the crew’s instructions and recommendations in order to ensure the security and safety of the aircraft, the smooth running of the flight and the comfort of the Passengers. The Passengers must, in Carrier’s reasonably opinion, refrain from behaving in such a manner to which other Passengers may reasonably object.
4. Smoking (including conventional cigarettes, electronic- or other artificial forms of smoking) is strictly prohibited on board the aircraft.
It seems that there is this underlying movement to decide that rules are not to be followed and can be challenged.
If you have an issue with an airlines rules why not write to them?