153.—(1) As soon as may be after the issue of a warning letter under section 152, the planning authority shall make such investigation as it considers necessary to enable it to make a decision on whether to issue an enforcement notice F657[or make an application under section 160].

(2) (a) It shall be the duty of the planning authority to ensure that decisions on whether to issue an enforcement notice are taken as expeditiously as possible.

(b) Without prejudice to the generality of paragraph (a), it shall be the objective of the planning authority to ensure that the decision on whether to issue an enforcement notice shall be taken within 12 weeks of the issue of a warning letter.

(3) A planning authority, in deciding whether to issue an enforcement notice shall consider any representations made to it under section 152(1)(a) or submissions or observations made under section 152(4)(b) and any other material considerations.

(4) The decision made by the planning authority under subsection (1) including the reasons for it shall be entered by the authority in the register.

(5) Failure to issue a warning letter under section 152 shall not prejudice the issue of an enforcement notice or any other proceedings that may be initiated by the planning authority.

F657[(6) F658[…]

F659[(7) Where a planning authority establishes, following an investigation under this section that unauthorised development (other than development that is of a trivial or minor nature) has been or is being carried out and the person who has carried out or is carrying out the development has not proceeded to remedy the position, then the authority shall issue an enforcement notice under section 154 or make an application pursuant to section 160, or shall both issue such a notice and make such an application, unless there are compelling reasons for not doing so.

(8) Nothing in this section shall operate to prevent or shall be construed as preventing a planning authority, in relation to an unauthorised development which has been or is being carried out, from both issuing an enforcement notice under section 154 and making an application pursuant to section 160.]]