21.—(1) The chief constable shall cause to be published, in accordance with this regulation, annual duty rosters for members and in these regulations—
(a)a reference to a rostered rest day is to be construed, in relation to a member who is required to do duty on that day, as a reference to a day which according to the duty roster was, immediately before he was so required to do duty, to have been a rest day for the member; and
(b)a day off granted in lieu of a rostered rest day shall be treated as a rostered rest day.
(2) Each such roster shall be published at intervals not exceeding 12 months and not later than one month before the date on which it is to come into force.
(3) Each such roster shall set out, for the 12 months following the date on which it comes into force, in relation to each member to whom it relates—
(a)his rest days;
(b)those days, being public holidays, on which he may be required to do duty; and
(c)the times at which his scheduled daily periods of duty are to begin and end.
(4) Subject to paragraph (5), a duty roster shall make provision for—
(a)an interval of not less than 8 hours between the ending of each of a member’s daily periods of duty and the beginning of the next; and
(b)an interval between each of his rostered rest days not exceeding 7 days;
unless the central committee agrees otherwise.
(5) Where, owing to the exigencies of duty, it is necessary to alter a duty roster, the officer responsible for making the alteration shall endeavour, so far as practicable, to avoid thereby requiring a member to do an additional daily period of duty such that the condition in paragraph (4)(a) would not be satisfied in relation thereto.