It depends entirely upon condition.
A non original box will not add value I am afraid - neither will the scope rail.
A good condition one with original box, scope rail and scope would probably get about £250.
A simple pistol in good condition with the fore end marked "Hurricane" £180 - rather than "Webley Hurricane" maybe £150.
These are just average figures - as I say condition is all and immaculate examples go for much more.