Almost certainly an antique, in which case can be held without FAC, provided that you do not intend to fire it. You can hang it on the wall if you want to.
If you do intend to fire it than it is either (if rifled) S1 or SGC (if smooth - even if you would fire single ball or bullet)
The law is a bit odd here, since you could have a pair of near perfectly identical antique guns, one of which you shoot, so it is on FAC and must be kept locked up etc., and the other you do not fire so you can hang it on the wall!
Would take a lot more detail to be sure, as it could be a reproduction and these are all S1, however this is unlikely since it would probably be on someone's FAC. Did you get a maker's name?
Could be an interesting piece as it might have started out as a flintlock and been later converted to percussion (it was not uncommon for owners to "upgrade" their guns as technology changed).
If you are looking for a wall hanger, then a gun in non-firing condition (usually rusted or badly pitted) can be had for less than £200, depending upon how nice it is.
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