Knowing that the original security fence still existed I thought I'd have a wander around the perimeter and hope for a bit of luck.
I got it in bucketloads.
I stumbled upon an area a bit larger than a football pitch which was crushed brick and concrete with a few plants, and which held a couple of dozen Grayling.
Number 31 in The Quest.
The Grayling are in the area to the right of where I took the pic below and on the banking in view
Two of the Grayling seemed to be doing a bit courtship which involved rapid opening and closing of wings so I took shots as quick as possible and luckily got an open overwing picture