Boslandew,
I worked in the Buzzard Cell at BBK in the late '80s and the limit in use then was 100' cloudbase and 1000 metres vis.
In practical terms there was a lone tree on the ridge to the east of BBK. If the tree was visible then all normal operations - trash, pax etc went ahead.
Taskings were not broken down by type as the most efficient usage of hours saw a cab tasked to do several different tasks in one go.
Separately:
If you take Mr Holbrooke's statement that he could see the wall of the lighthouse at the base of the cloud and contour that round to where it intercepts the Boeing simulation you find that the position of the waypoint change is 973m from the cloud covering the hill.
EG