3 trigger SxS identifying

[Hunterwill]

Need some help identifying this curiosity. Stamped London fine twist on the barrel. Under seems to have English insignia with the crossing lances. And I believe a EP. The front trigger is rear facing and is used to open the action. Seen a Steven online that has 3 triggers, the barrels look similar but the action looks different. Have not seen one the same as this. Other than that have no idea who makes this thing or the value. Any ideas?

See link for pic and vid of the gun
https://www.dropbox.com/s/gwfyt5y0oltxmje/Photo 2020-12-15, 8 54 13 PM.jpg?dl=0

https://www.dropbox.com/s/20o8ekrhjid9645/Video 2020-12-15, 9 05 31 PM.mp4?dl=0

 

[Londonshooter]

This is sure ringing a bell for me but I cannot find a reference in my library. It looks like the locks are non-rebounding so you should put on half #### to open and close the action.
Mark description sounds like Birmingham proof house.
No maker's name on the sideplates or rib?
Like it a lot, thanks for sharing.

 

[Alex McKr]

Looks like there may be a maker's mark, on the barrel rib. What does it say? This should help narrow down the search.