The Firearms Act: Section 21
Section 21 of the Firearms Act prohibits the possession of a firearm and ammunition (under any circumstances), by any person who has been convicted of a crime and sentenced to a term of imprisonment (or its equivalent for young persons) of 3 months or more. The prohibition applies in all circumstances, including handling and firing at an approved shooting club or at a clay pigeon shoot where a certificate is not ordinarily required. It also applies to the possession or use of other categories of firearms and ammunition such as airguns or shot gun cartridges for which a certificate is not needed.
A sentence of 3 months to 3 years attracts a 5 year prohibition, a sentence of greater than 3 years attracts a life time prohibition.