One of those annoying negatives. The envelope said 5752 Chipping Norton, it clearly is a Large Prairie but the location is correct. With all those photographers there must have been a special due as surely they were not waiting for a two wagon freight hauled by a Prairie without a front numberplate. The only clue to the locos identity is a stenciled 84A and those painted hinges..
Vic Smith helps out - "Most probably 1963-09-14, awaiting the REC “The Chilten 200” hauled by 6111. There were very few 51xx locos left at that time, so could be Worcester’s 5152, previously allocated to 84A, which was withdrawn two month later" - the condition fits perfectly and an easy mis-read of 5752.