You should not have taken that out of its box, it is one of only three ever made. You clearly don't know what it is.
Far from being a pound-shop buy, it is one of the rarest fixed-projectile airguns - the Hartlepool Monkey-Spanker. I think you should give it up to your local museum. The production and distribution of this ingenious design was halted after a top-level intervention by the Government. The French were apparently appalled, and demanded it withdrawn.