I have just had a good look at the mag housing, Vincent, but can't see a S.A. marking. It just has Sten M.C. MKIII on the top and L.B. & the serial on the lower face. Were the S.A. markings normally on the upper or lower face? The overall finish is a good painted surface although part of the rear receiver has rusted in the past but appears to have been treated and the whole Sten then repainted. I can't see any other markings visible.