Nice one chaps. Got it sorted. It seems that that little screw in fella doesn't actually screw into anything. The thread bit has a hole for a tiny allen key so all I had to do was cut the straddle cable, thread it through the hole and the tighten up that little allen key thread ooojit when the cable was the right length. I now have a working rear brake.
Although I've gone for a left hand lever and I'm not totally convinced I like that.