One thing I've been surprised at doing my house is that getting a plasterer is easier and cheaper than you might have thought. So, be brave.
Take down the bits of ceiling and wall that are in the way, drill proper holes in the joists and noggins for the cable runs and lay the cable in. Wire up the other end of the cable, then tape over the ends of the cable where the wall lights will go.
Next get some plasterboard -- B+Q usefully sell it in half-size sheets that fit in a car -- cut to the size of your holes (with little holes for your cables), and nail to the joists in the ceiling and the noggins in the wall. Don't worry too much if there's a few mm around the gap, it doesn't need to to be too precise.
Then have a plasterer put a "skim coat" over the top of the lot. He or she may even say it's cheaper and easier for them to do the whole ceiling or the whole wall. Stand back open-mouthed while they do the lot in a few minutes!
Oh, and I'd take @Tim Baker's suggestion of picking up the power from the switch. Given that you're in the UK, if the wiring was done in the last forty years this is going to be a pull switch on the ceiling, no?
(Usual disclaimers apply: be careful mucking about with power in the bathroom, it makes sense [and is required by the Building Regs] for a circuit that's going to a wet area to be protected by an RCD.)
It does need to be protected there by the sink. It may very well be wired into the LOAD terminals of the other GFCI outlet. It is easy for you to check. Plug a lamp in by the sink and turn it ON. Then press the TEST button on the GFCI outlet. If the lamp goes OFF you know that the outlets are coupled.
Best Answer
All receptacles in a bathroom are required to be GFCI protected. As far as the location away from wall there is no requirement on that it could be touching the I have put them in a corner touching or almost touching 2 walls.