Sure Essex is a big place but when I just googled it there seems to be a good choice of E-cig shops around the area.
For example: http://www.essexecigstore.com/
Jetpilots advice is spot on Dan imo.
You really need to take him to a shop so that he can experience a load of different flavours to find something he likes. Not sure how much of this thread you've read but I used to smoke cigarettes, then went on to vaping and now I've managed to quit altogether.
Took me just over a year and a bit from stopping the fags, starting vaping, slowly reducing my E-liquid nicotine levels till eventually I was using zero nicotine E-liquid & then stopped vaping completely.
Wasn't a walk in the park & I still get the odd cigarette craving but I'd have never been able to do it without using the E-cigs. If your Dad gives it a good go then I'm sure he'll be able to do the same.