Electric is fine for city cars - and presumably most of your travel is within London, but long distance its still not effective. To get those ranges, you've probably got to travel at something like 50MPH, so its already taking longer, then every hour and a half's travel actually takes 2 hours because of the charge time.
Not sure if it would be better or worse over here. Towns can be an hour apart over here - so you're probably going to need to charge when you're only down to 50%, but there again I suppose its easier to create unmanned fill up points anywhere there's a power feed, so as there's so few roads, they could easily be installed in in the middle of nowhere.
Anyway, they are not green at all. The batteries are environmentally toxic to make and the electric you'll be using will have primarily been created from coal (at least here would be green hydro). The cost savings on fuel, will be offset by hugely expensive battery replacement costs as their life, although getting better, is still quite short.
Calling them 'green' should be directed to the advertising standards authority.