This is a fabulous pistol. The more I study the photos, read the comments from other members and have a think about it, the better it gets!
The trigger design could be improved by way of an independent sear and the trigger-guard made thicker and sculpted as it would no longer be employed as a spring.
I'd also angle and re-style the grip, although it does need to be relatively upright to perform its arc-forming cocking stroke. Similar in orientation to the grip- cocking designs mentioned in previous posts.
Back to what it is though, being the theme of this thread discussion- not how it could be 'developed'!...
You mention John, the possibility that the inscription could be faked in order to confer enhanced value.
In the absence of documentation this has to be considered.
The faker is putting it out there to challenge the records the motive being profiteering, mischief-making, or both.
Enhanced value would be maximised by using illustrious names such as Westley Richards, Cogswell and Harrison and Greener. I use these examples as being widely known makers of good shotguns who have had minor and short-lived but eclectic, high-end dabblings with airguns.
A speculator at auction or wherever, not expert in either field would nonetheless know these makers and may feel comfortable in paying more.
Would greater value be conferred by Frank Clarke, BSA, LJ et al?...
Am I correct in believing that BSA made some weird and wonderful prototypes, or pieces that are widely acknowledged to be from the factory and left them un-marked? as did Webbo?...would they annoint some prototypes and not others? An unanswerable question...Maybe workers would nab a prototype and stamp it at home in which case it would be the real deal but not 'sanctioned' by their employers.
Was it standard factory practice to have their identity on tested products destined for market only, not something under test that may or had failed?
Would prototypes be made with the intention of destroying them or putting them un-marked in a locked room if they did not make the grade- maybe unearthed years later to be sold, as Webley did back-along
A forensic examination of the lettering is helpful.
Oh dear!...That's got me thinking about your LP52 Danny...