ok power transmission i can explain
standard over head power cables or equivalent, lose approximately 10% of the power put into them for every 100 miles of cable...
i.e. moving power from mid Scotland to London 50% is lost in transmission mainly as heat (there's that global warming thing again) so imagine how much you'd have to put into move it from Africa.
the reason power comes from France to southern England is because its closer than Scotland and easier to get power from.
secondly if you have been following the issues of getting a new set of heavy duty overhead cables run from Scotland to England you'll know for every NIMBY that doesn't like either nuclear power or wind turbines there are approximately 47* that will object to power lines.
Scotland produces more power than it needs particularly if the wind is blowing

but at the moment we can't get enough of it out of the country to offset the shortfall of power in the south of England!!!
The obvious point from all this is we lack capacity to generate in southern England but obviously that cant be fixed because that's where all the politicians and they're buddies live...
*not a proven number but sure feels like it...