This is the 7.30.a.m. Westcountry express from Paddington to Kingswear (with, I think, a couple of coaches detached at Newton Abbot for Plymouth) running the "long way round" into Bath Spa here in this view and then on to Bristol.
5056, "Earl of Powis" is one of Old Oak Common's allocation of "Castles" and she will probably work right through to Newton Abbot or Kingswear, as this was often the case at this time, the engine carrying sufficient coal for such an extended run and being able to take water by means of the troughs at Exminster together with station watering facilities at Temple Meads and Exeter St. Davids.
5056 spent many years at Old Oak, later going to Wales, Hereford and Wolverhampton from where she was withdrawn in November 1964.