17(1) A constable [or designated person] may enter and search any premises for the purposes -
(a) of executing -
(i) a warrant of arrest issued in connection with or arising out of criminal proceedings; OR
(ii) a 'warrant of commitment'
(b) of arresting a person for an indictable offence;
(c) of arresting a person for an offence under -
(i) section 1 of the Public Order Act 1936 (prohibition of uniforms in connection with political objects);
(ii) any enactment contained in sections 6 7 8 or 10 of the Criminal Law Act 1977 (offences relating to squatting and unlawful eviction)
(iii) section 4 of the Public Order Act 1986 (fear or provocation of violence);
Note: This power does not apply to section 4A.
(iiia) section 4 (driving etc, when under influence of drink or drugs) or section 163 (failure to stop when required to do so by constable in uniform) of the Road Traffic Act 1988;
(iiib) section 27 of the Transport and Works Act 1992 (which relates to offences involving drink or drugs);
(iv) section 76 of the Criminal Justice and Public Order Act 1994 (the offence of failure to comply with an interim possession order).

C(a) of arresting, in pursuance of section 32(1A) of the Children and Young Persons Act 1969, any child or young person who has been remanded or committed to local authority accommodation under section 23(1) of that Act;
C(aa) of arresting a person for an offence to which section 61 of the Animal Health Act 1981 applies;
C(ab) of arresting a person under any of the following provisions -
(i) section 30D(1) or (2A); (ii) section 46A(1) or (1A);
(iii) section 5B(7) of the Bail Act 1976 (arrest where a person fails to surrender to custody in accordance with a court order);
(iv) section 7(3) of the Bail Act 1976 (arrest where a person is not likely to surrender to custody etc);
(v) section 97(1) of the Legal Aid, Sentencing and Punishment of Offenders Act 2012 (arrest where a child is suspected of breaking conditions of remand);
c(b) of recapturing any person who is, or is deemed for any purpose to be, unlawfully at large while liable to be detained -
(i) in a prison, remand centre, young offenders institution or secure training centre, OR
(ii) in pursuance of section 92 of the Powers of Criminal Courts Sentencing) Act 2000 (dealing with children and young persons guilty of grave crimes), in any other place;
(d) of recapturing any person whatsoever who is unlawfully at large (e.g. a patient who has escaped from involuntary custody at a Mental Hospital) and whom he/she is immediately pursuing.
(e) of saving life or limb (human) or preventing serious damage to property.
Note that animals may be property.

Conditions allowing search and extent of search
17(2) Except for the purpose saving life and limb, the powers of entry and search conferred by this section -
(a) are only exercisable if the constable [or designated person] has reasonable grounds for believing that the person whom he is seeking is on the premises;
AND
(b) are limited, in relation to premises consisting of two or more separate dwellings, to powers to enter and search-
(i) any parts of the premises which the occupiers of any dwelling comprised in the premises use in common with the occupiers of any other such dwelling; AND
(ii) any parts of the premises which the occupiers of any dwelling comprised in the premises use in common with the occupiers of any other such dwelling; AND (ii) any such dwelling in which the constable [or designated person] has reasonable grounds for believing that the person whom he is seeking may be there.
17(3) The powers of entry and search conferred by this section are only exercisable for the purposes specified in subsection (1)(c) (ii) and (iv) by a constable in uniform.
17(4) The power of search conferred by this section is only a power to search to the extent that is reasonably required for the purpose for which the power of entry is exercised.

Indictable offence

Includes offences that are triable either way. Remember - these offences exclude the likes of TWOC and Section 5 Public Order Act as these are Summary offences.

Breach of the Peace

Nothing in this section affects any power of entry to deal with or prevent a breach of the peace. However, all other common law rules under which a constable had a power to enter premises without a warrant have been abolished.

Community Support Officers

A suitably designated Community Support Officer (CSO), under paragraph 8 of Schedule 4 to the Police Reform Act 2002, has the same powers of a police constable under section 17(1)(e) above, namely to enter and search premises for the purpose of saving life or limb or preventing serious damage to property.

Warrant of Commitment

A commitment warrant to prison issued under section 76 of the Magistrates' Courts Act 1980 (for failure to pay fines); it does NOT include 'default warrants' where an offender has defaulted on his/her payment of a fine etc. and is being ordered to appear before a Court to explain the reasons.