Image of (Colchester branch staff?) in costume on a stage

Photograph showing a group of men and women on a stage wearing various costumes. Since the photograph had been put in the Colchester branch image file, it is assumed that the people on the stage are staff from Colchester branch (however, there is no description on the back of the photo to confirm this). This might possibly be the photograph of the "JS concert party for the Royal Engineers before going abroad 1939" which is referred to on a letter from Bill Steggles which was found with SA/BRA/7/C/31/1/12 or could be some other theatrical performance involving staff from the branch.