From researchers who have connections to "manufacturers of smoking cessation medications".
There is very little risk of nicotine toxicity from major electronic cigarette (EC) brands in the United Kingdom. Variation in nicotine concentration in the vapour from a given brand is low. Nicotine concentration in e-liquid is not well related to nicotine in vapour. Other EC brands may be of lower quality and consumer protection regulation needs to be implemented, but in terms of accuracy of labelling of nicotine content and risks of nicotine overdose, a regulation over and above such safeguards seems unnecessary.
These are good things - people really are stopping harmful smoking with them. So let's encourage rather than carp and condemn, eh?
H/T Dick Puddlecote