SECTION 21 OF THE FIREARMS ACT
 

Possession of firearms by persons previously convicted of crime.
(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 offender institution for such a term, or who has been sentenced 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 three years or to youth custody or detention in a young offender 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 or who has been subject to a secure training order or a detention and training order, 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.

(2A) For the purposes of subsection (2) above, “the date of his release” means—
(a)in the case of a person sentenced to imprisonment with an order under section 47(1) of the Criminal Law Act 1977 (prison sentence partly served and partly suspended), the date on which he completes service of so much of the sentence as was by that order required to be served in prison;

(b)in the case of a person who has been subject to a secure training order—
(i)the date on which he is released from detention under the order;
(ii)the date on which he is released from detention ordered under section 4 of the Criminal Justice and Public Order Act 1994; or
(iii)the date halfway through the total period specified by the court in making the order, whichever is the later.
(c)in the case of a person who has been subject to a detention and training order—
(i)the date on which he is released from detention under the order;
(ii)the date on which he is released from detention ordered under section 104 of the Powers of Criminal
Courts (Sentencing) Act 2000; or
(iii)the date of the half-way point of the term of the order,
whichever is the later.
(d). . . . . . . . . . . . . . . .
(2B). . . . . . . . . . . . . . .

(2C)Where—
(a)a person has been sentenced to imprisonment for a term of three months or more, and (b)the sentence is suspended under section 189 of the Criminal Justice Act 2003, the person shall not have a firearm or ammunition in his possession at any time during the period of five years beginning with the second day after the date on which the sentence is passed.