Going by its number it came from one of the Pre-grouping companies that became part of the LNER..
Thats it all I can tell you! Looks like it could be a Great Eastern coach though.
DE320781 was formerly an NER BZ, number E2144E, built in 1918.
It was listed in the 2nd edition of "Departmental Coaching Stock" ( Platform 5 ) in April 1985, but not listed in the third edition dated June 1987.