trace

The electrician will be along soon enough to stick some wires down the insides of the walls in advance of the work on the meter, whereupon he can hopefully poke about a bit to determine what, if anything, this is doing. It could possibly be the supply to the garage routed round the back of the house, but might also be supplying the kitchen as that's where it appears to re-enter the house after its journey around the east wall.