As of this date there are no clear restrictions on these products' import into the UK, but they are moving towards having it banned, based on the latest reports I have seen (and no definite outcome yet) Link hidden: Login to view
Nevertheless I have also learned that most of the imports were from China, aside from the fact that there are UK based companies manufacturing e-cigarettes.
We haven't received any complaints against E-cig as of to date. We suggest that you do a test purchase to confirm if they will satisfy your requirements.
Let us know how you get on and if you need further help.