I expect it's 317512 and possibly 317503 as well. The former is PRM modified but had severe corrosion. I suspect some carriages may have swapped between units to make one good unit.This movement is currently underway. I believe it's a refurbished 317 hauled by a DRS locomotive (class 57?) but it was a bit dark when I saw it!
Realtime Trains - 579I 0900 Kilmarnock Bonnyton Depot to Ilford E.M.U.D.
Realtime Trains provides live realtime running information for the Great British railway network using open data.www.realtimetrains.co.uk