BR Riddles 'Standard Britannia' class 4-6-2 No. 70022 'Tornado'. Built at Crewe in August 1951 and withdrawn in December 1967.
Exeter St. David's was originally a Brunel designed GWR station and the L&SWR had running rights. Hence the appearance of both ex-GWR and ex-SR locomotives in the steam era. British Railways added their fleet to this mix and here is immaculate 'Tornado' (no-not THAT one!) in the station in July 1953.
Peter Kerslake adds "Newton Abbot's 70022 is on a return "North to West" working".