A gun like yours in its condition would sell in the UK for £120 sterling that would be $240
I think it would cost almost that much to ship it back to the UK.
Fortunately or unfortunately, they go for about twice that over here. But I think they got used much more here as well, and tend not to survive in good condition, as Captchee alludes to in his post. Over there, shooting was largely limited to the upper classes and those employed by them, whereas in the U.S., every farm boy had a shotgun.
I would guess that you see more rust and neglect related to storage when the gun was no longer useful, while here, they were used until they literally fell apart.