The trouble with this photograph is that it is undated and nearly head on and it is difficult to see the locomotive sides. However, I can see that it has half-green deflectors and with SOUTHERN on the tender side which narrows the date down. It could possibly be August 1939 just before the outbreak of WWII, but I would suggest it is post-war between July 1946 when it was repainted in post-war Malachite and April 1950 when it received its BR livery.

Further correspondence reveals the headboard that is carried was only used between October 1946 and the Summer of 1948. Apparently the background was a dark green with a yellow edge and yellow with black shading letters.