I've just checked the sling mounts, stamped P.H & sling is stamped made in england
In the OP, you asked for a valuation. My guess - & I'm no expert - with those interesting period extras - £250 to £300 in a private sale.
ATB
Bru
Webley Mk3 x2, Falcon & Junior rifles, HW35x2, AirSporter x2, Gold Star, Meteors x2, Diana 25. SMK B19, Webley Senior, Premier, Hurricane x 2, Tempest, Dan Wesson 8", Crosman 3576, Legends PO8.