17.—(1) The holder of a Great Britain certificate may, subject to any applicable conditions, have in his possession in Northern Ireland any firearm and ammunition to which the certificate relates if—
(a)he has provided the Chief Constable with such information about that firearm and ammunition and such other information as the Chief Constable may require; and
(b)he holds a document authorising that possession issued to him by the Chief Constable.
(2) A Great Britain certificate shall not continue in force in Northern Ireland by virtue of paragraph (1) for a period longer than that for which it was granted or renewed in Great Britain.
(3) The Chief Constable may at any time require the holder of a certificate of approval to surrender it.
(4) In this Article—
“applicable conditions” means the conditions under which the Great Britain certificate is held, subject to such modifications as may be specified in the certificate of approval;
“certificate of approval” means the document issued under paragraph (1)(b);
“Great Britain certificate” means a firearm certificate or shotgun certificate granted in Great Britain;
“modifications” includes additions and omissions.
18.—(1) A person resident in Great Britain may, without holding a firearm certificate, have an air gun in his possession in Northern Ireland if—
(a)he may have the air gun in his possession in Great Britain without a firearm certificate by virtue of section 1(3)(b) and (4)(b) of the Firearms Act 1968 (c. 27);
(b)he has provided the Chief Constable with such information about the air gun and such other information as the Chief Constable may require; and
(c)he holds a document (“a certificate of approval”) authorising that possession issued to him by the Chief Constable.
(2) The Chief Constable may at any time require the holder of a certificate of approval to surrender it.