..is knackered.

It was seemingly caused by me cleaning the inside of the back window with window cleaner..but surely something so minor wouldn't cause any problems??

The 2 wires aren't broken? (very common problem!)

I seem to remember reading in the owners manual never to rub vertically, always horizontally, as they can be damaged very easily! Also as Duvel says, the wires are very vulnerable, they're normally always bodged, replaced or getting close to breaking! Pete

Which two wires would they be?

either chack the ones at either side of your rear window or where they pass through from the rear hatch into the body to start with.