It is certainly a BSA, they were all made with an action body shape similar to the Facile Princeps but were of course A&D actions.
Note the action shape and screw and pins placement on the BSA BLE “specially made for Fletchers of Gloucester”.
And the shape of the bottom plate (loads of room for engraving).
Dovetailed chopper lumps.
Sooo … inside my £150 (if I am lucky) BSA lurks a $6,995 best boxlock just waiting to be liberated by a good action filer, engraver and stocker (the existing walnut, straight grained with a “fiddle back” ain’t bad).
I believe BSA directors and senior employees may have used De Luxe models.
I wonder if one of them made this anonymous example as a “show and tell” gun - “Who do you think made this?”