Unidentified GWR King Class 4-6-0 (at Southall)

It was 1964 when my friend Harry gave me this photograph. I have long since lost contact with him. I have always assumed the locomotive was a King but I suppose it could be a Castle. Can anyone tell me which it is? Secondly does anyone know where the photograph was taken? Any help would be gratefully received (I now know this is a King at Southall)

Done