Thanks all, I've never seen many escutcheons engraved either, certainly not this nicely.
The top rib simply has the 16 new Oxford Street London.
Yes there is Deeley and edge patent stamped on the side of the forend latch.
Presumably then its a bespoke gun due to its unusual configuration, a heavy 12 bore half pistol grip that was made without choke.
Possibly also with 3 inch chambers. If they have been lengthened it was done many years ago, wall thickness at the chamber end is around 95 thou.
I seem to recollect seeing a gun with BALL stamped underneath, was this done at all when they were stamping "not for ball"?
Irrespective of chamber the weight and lack of any choke would suggest a specific purpose, and I'm guessing it was not uncommon to fire ball ammunition at the time, do you think it could have been for this purpose?