Doubles are certainly allowed in the UK. The chief constable (head of police) of the county must give his approval (signature) to the individual owning any firearms. This is done through his firearms department. To get approval you must prove valid reason to own and use a firearms in any calibre. In most cases this involves proving you have suitable land and quarry for the rifle, be this land you own and suitable quarry for the calibre in question; or you rent/have permission to use the land and have suitible quarry for the calibre; or you can prove you have an invitation (commercial or private) to shoot a suitable quarry for calibre either in the UK or abroad.

If no valid reason is given, or your reason is not deemed to be good enough by the police, they will refuse you application for a firearm. I know enough people who have doubles. Most are of old title families with large estates and/or land abroad. The others I know of are generally people with money and time to spend in Africa; or those close to the gun trade with the passion for Africa.

Oh to have the freedom of America's firearm laws!