21.—(1) A declaration of a zone under these Regulations—
(a)must be in writing;
(b)must designate the extent of the zone being declared;
(c)may be amended or revoked by further declaration at any time.
(2) Unless the Welsh Ministers state otherwise in any declaration of a zone, any movement which is prohibited but has already started when such a declaration comes into force may be completed.
(3) Any person on whom a restriction or other measure is imposed by virtue of a declaration under regulation 17(5), 18(9), or 19(3) must comply with it.
(4) In deciding to amend or revoke any declaration of a zone, the Welsh Ministers must have regard to the epidemiological situation and the measures necessary to control the spread of African horse sickness virus.