That rear-sight leaf tells you everything! You have a Khyber Pass gem. (Not BritishMade)!
For $30 you have a great conversation piece.
It is Decorator Only/Never To Be Fired, but, fascinating as can be. Go easy on the cleaning, the patina will be part of its charm.
I would recommend #0000 steel wool saturated with mineral spirits followed by Hoppe's #9 on the metal. Go lightly and know when to stop.
Rub down wood with cotton rags damp with 50/50 mix of linseed oiland turpentine. Finish with rubs of Howard's "Feed & Wax".
Just go for stabilization and character.
You have an interesting handmade fake of a British Military Arm.
(Dispose of rags properly to avoid spontaneous combustion).