This is what the latest Home Office Guidance states.
13.58 The collecting of firearms by a genuinely interested collector should be accepted as a
“good reason” for the grant of a firearm certificate. There should be no blanket policy to
prevent the collecting of modern firearms (though collectable firearms will tend to be of the
Second World War or earlier eras) nor should arbitrary limits be imposed on the number
or type of firearms. However, a single firearm is unlikely to be acceptable unless it forms
part of a collection of other exhibits (but see chapter 9). Modern reproductions of vintage
arms may be collected, especially to fill gaps in collections of older firearms. There are
no calibre-based limits for collecting, and collections may include field artillery, tanks and
other armoured fighting vehicles. Vintage handguns are dealt with in chapter 9. Collections
may include firearms disguised as other objects that would otherwise be prohibited
under section 5(1A)(a) of the 1968 Act. Ammunition may be collected of itself, including
expanding, incendiary or armour-piercing ammunition or explosives that would otherwise
be prohibited under section 5(1A) of the 1968 Act.
13.59 Chief officers of police should satisfy themselves that the applicant is a bona fide collector
who has a genuine interest, perhaps academic, in the evolution of firearms or in particular
types or periods, and that the types of firearm requested fall within this interest. Evidence
that a person is a member of a relevant society (for example the Historical Breechloading
Smallarms Association or the European Cartridge Research Association) might be taken as
an indication that they have a genuine interest in collecting, but this is not a requirement.
Firearms capable of being fired may be collected, and a collection may include items
other than firearms, for example, uniforms and military equipment. Collections of one
or two firearms should not normally be accepted unless they form part of a wider
collection of non-firearm related exhibits. “Collection” should not be used as an excuse
to retain firearms purely for personal or sentimental reasons. In the case of Hutchison v
Chief Constable of Grampian’ (1977), the Court upheld the decision to refuse to issue a
certificate for collection to an applicant who was not considered to be a bona fide collector.