(1) A person who has been sentenced (to custody for life or) to preventive detention, or to imprisonment or to corrective training for a term of three years or more (or to youth custody (or detention in a young offenders institution) for such a term), or who has been sentenced to be detained for such a term in a young offenders institution in Scotland, shall not at any time have a firearm or ammunition in his possession. (2) A person who has been sentenced…. to imprisonment for a term of three months or more but less than 3 years (or to youth custody(or detention in a young offenders institution) for such a term), or who has been sentenced to be detained for such a term in a detention centre or in a young offenders institution in Scotland, shall not at any time before the expiration of the period of five years from the date of his release have a firearm or ammunition in his possession. This means: Section 21 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 three 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 normally required. It also applies to the possession of other categories of firearms and ammunition such as AIRGUNS or shot cartridges for which a certificate is not needed. A sentence of 3 months to 3 years attracts a 5 year prohibition, shorter ones no prohibition but a longer one means a life ban.