Two weeks later I finally got to go up there.

I managed to look for 30 mins about 100m to far West, then realised someone might have got two digits round the wrong way in their 8 figure grid ref *cough*

Anyhoo I found it eventually :) Grid ref of SU **** ***** according to the GPS. I've got one for the Polisher too, Pete is within a 100 metres or so...