The issue about how to charge a much larger population of electric cars is one which apparently the UK electricity network isn't too worried about. I read a report recently what said that while the demand will be much higher, most of that will be at night, and it'll be much more predictable and indeed controllable than existing demand. For example, if half the houses in the country have electric cars charging up outside them overnight, then it's likely there will be the ability for the electricity network to dial down the charge rates up and down in real-time as other demand peaks and troughs. As most cars won't take all night to charge, they can do so at the times best for the electricity supply.
There was even talk of using the UK electric car network as a great big battery to supply the grid when needed, reducing the need for power stations to over-supply (which they do at the moment), though I think that was more of a concept than a properly thought through idea.
