Thanks for the effort Spidge; I appreciate how time consuming it is to search that many entries, and then still not have a definitive answer. Made some progress today. We went to see our Home Guard contact again, and after the first visit he had dug out his copy of the Finn book mentioned by Harry and David. He confirmed that the crash location was the farm mentioned on page 22, and the description of one crewman surviving the crash but dying of wounds before daylight matches with what he said. The son of the farmer who ignored the shouts still lives in the village, so it's something only spoken of in whispers.
I didn't get a chance to look at the Finn book in detail, but from the 'lost Bombers' website I found the most likely Hampden crash:
Serial Number
AD723 Squadron
61 X1D
QR-? Operation
Cologne Date 1
1st March 1941 Date 2
2nd March 1941 Airborne 2001 1Mar41 from Hemswell. Crashed in bad weather, 0500 2Mar41 near Caistor, 11 miles SW of Grimsby, Lincolnshire. Sgt K.G.Cooper KIA Sgt W.Windle KIA Sgt M.Gough KIA Sgt G.Hall KIA " The only thing I'm not sure about was another page in Finn which mentions fire being seen in the sky before the crash, which would suggest enemy action, although this could have been another incident. Still no luck on the Airspeed Oxford...