The law in this respect in he UK is quite simple and needs to be explained. Here goes:
Section 58 of the Firearms Act 1967 allows for certain types or calibre of gun to be held as curiosities and/or for display only. For this you need NO LICENCE AT ALL. So, you can have an 8-bore hammer shotgun, or a 12-bore pinfire, or a .450 BPR double rifle without any licence requirement.
If you want to shoot shotguns, you need a shotgun licence and the guns need to be on that licence. So, if you want to take that 8-bore hammer gun off the wall and shoot ducks with it (which we can do in the UK), you just need to put it on your shotgun licence.
That's it - a licence is needed if you want to shoot it - no licence if you just want to look at it.
