Hi again,
I have one of those yellow plastic double wall box drilling jigs somewhere (you attach it to the wall then 'chain drill' though the holes in the plastic block.
I remember it working pretty well, particularly as you could depth stop the drill so the back of the box was pretty true / constant?
I looked in Wikes / Homebase tonight but they don't do them?
Where next?
All the best ..
T i m
Go on then .. what do we do 'nowdays' (and non the SDS box smasher) .. ;-)