Prison rules, that is to say, rules made under section 47 of the Prison Act 1952 (c. 52), may include provision for the award of additional days—
to fixed-term prisoners, or
conditionally on their subsequently becoming such prisoners, to persons on remand,
who (in either case) are guilty of disciplinary offences.
Where additional days are awarded to a fixed-term prisoner, or to a person on remand who subsequently becomes such a prisoner, and are not remitted in accordance with prison rules—
any period which he must serve before becoming entitled to or eligible for release under this Chapter,
any period which he must serve before he can be removed from prison under section 260, and
any period for which a licence granted to him under this Chapter remains in force,
is extended by the aggregate of those additional days.