Markus--I can't offer any help as to whether this is a screw grip based only on that photo. What I can tell you is that Webley & Scott used the screw grip action for a very long time. I owned a Webley & Scott boxlock, model 400 (Grade 1--the highest grade of that model). By the SN, it was made in 1924, and it was on the screw grip action. The Model 400 was in production until just after the end of WWII, when W&S replaced it with the Model 700.
I've also owned A&N's, and have received copies of the pages from their records on my guns. I would suggest that you request that information, because it's well worth the cost.
Once you have the gun in hand, you can tell very easily if it's a screw grip. Remove the barrels and look in the slot in the breech face. Rotate the top lever. You will be able to see the threads on the piece that engages the rib extension (which can be either a doll's head as on this gun, or a straight extension, as it was on my Model 400.)
Last edited by L. Brown; 08/21/18 11:59 AM.