Not in a position (too young!) to answer the questions but it may help if I pose two more? What distance from the airfield did the crash happen? Was QNH used in 1941, as opposed to QFE?
3 miles downwind would be about right for a 3 deg approach.
Oops, looks like crash was at 3 miles?
If you assume (and it is a big assume) that they were on a 3° approach, then they would have planned to be at about 900ft on the QFE at 3 miles out. If the crash was due to a simple altimeter setting error, the setting error would be about 22hpa - a big discrepancy that an experience pilot would probably have recognised even if he had not been in sight of the ground due to night and overcast conditions.