Just saw the launch of the new Tesla car, and at a claimed 215m to a
charge, I can see myself perhaps being persuaded to consider the
technology at some stage in the not near or medium future.

I have seen quite a few charging points (or whatever they are called) -
in most large European cities. I assume that the cost of a charge is set
so that it would be marginally lower to run such cars compared to
petrol/diesel cars.

But what would be a rough estimate for the true cost of a charge (i.e.
when done at home)?