A constable may enter and search any premises—
for the purpose of executing in England and Wales under section 136(2)(b) a warrant issued in Northern Ireland;
for the purpose of executing in Northern Ireland under section 136(3)(a) a warrant issued in England and Wales;
for the purpose of arresting a person in Northern Ireland under section 137(1) in respect of a relevant England and Wales offence;
for the purpose of arresting a person in England and Wales under section 137(3) in respect of a relevant Northern Ireland offence;
for the purpose of arresting a person in England and Wales under section 137A(1) in respect of a specified offence committed in Northern Ireland;
for the purpose of arresting a person in Northern Ireland under section 137A(4) in respect of a specified offence committed in England and Wales.
In subsection (1)—
“relevant England and Wales offence” means—
an offence that is an indictable offence in England and Wales;
an offence mentioned in section 17(1)(c) or (caa) of the Police and Criminal Evidence Act 1984;
“relevant Northern Ireland offence” means—
an offence that is an indictable offence in Northern Ireland;
an offence mentioned in Article 19(1)(ba) to (c) of the Police and Criminal Evidence (Northern Ireland) Order 1989 (S.I. 1989/1341 (N.I.12)).
The powers of entry and search conferred by subsection (1)—
are exercisable only if the constable has reasonable grounds for believing that the person whom he is seeking is on the premises, and
are limited, in relation to premises consisting of two or more separate dwellings, to powers to enter and search—
any part of the premises which the occupier of any dwelling comprised in the premises uses in common with the occupier of any other such dwelling, and
any such dwelling in which the constable has reasonable grounds for believing that the person whom he is seeking may be.
The power of search conferred by subsection (1) is only a power to search to the extent that is reasonably required for the purpose for which the power of entry is exercised.