Paul has sent me those photos and more questions than answers.
DA5574 is still an alive reg, showing on Carjam as a DD2.
Now, as Markson has said the photo is at Sutcliffes, I am going to take a wee leap to say the plates from the Buckler (DD2 being a version) made their way onto the de Joux coupe they are now with. I don't think that a DD2 chassis sits under that shell, as the side chassis tubes would impinge on the door openings.