"XK" was the squadron code for No. 272 Sqn from November 1940 until May 1941. It was also used by No. 46 Sqn from January 1945 to February 1950.
It has the look of a post-war photo. I can only see, I think, one respirator case. That it is a Dakota in the background indicates the latter dates given above, more specifically 1946 onwards. Sqn Markings_46