I recently visited the Pleydell-Bouverie family who kindly let me look through their photo albums.
Three photographs showed damage to the East Annex of Coleshill House caused by an explosion in 1942 or 1943. These can be seen by pressing '4' on the Coleshill site tour & layout page.
Wanted - any information or source leads relating to this happening
I can't help directly with the timing. However a couple of the soldiers are wearing Tam O'Shanters and another the Glengarry which indicates Scottish troops. I can't tell the regiment from the online pictures but there is one badge visible which might be identifiable if blown up from the original.
I see there are a couple of camouflaged sentry boxes and the photos show White painted patches or strips by all the entrances to help make them clearer in the blackout.