Guys, thanks for the replies. I was begining to wonder if I was the only one.

I have not yet found the answer either. Since my last post I have:
1) checked the trunk hinge wiring (looks ok)
2) been around all the bulb connections with a fibreglass cleaning pencil
3) checked the rearward wiring through the back of the trunk

I have now begun to pick my way through the wiring diagrams to try and work out where all these lights have common circuitry. The odd one out is the dip beam, which makes me think it must be the LKM or it's feeder wiring or alternativly, a positive power feed/fuse etc.

I'm hoping this one won't beat me