he may issue a warrant authorising the officer to enter the premises at any time (by force if necessary). If an authorised officer exercises these powers of entry, he may take onto the premises any other persons, and any equipment, that he considers necessary, and require a person present on the premises to provide him with any facilities, information, documents or records, or other assistance, that he may reasonably request. An authorised officer exercising these powers of entry shall, if so required, produce evidence of his authorisation under paragraph and any warrant before entering the premises or at any time before leaving the premises. An authorised officer, exercising these powers of entry, who enters premises which are unoccupied, or from which the occupier is temporarily absent, shall on departure ensure that all reasonable measures have been taken to leave the premises as effectively secured against unauthorised entry as he found them. Investigations into fires An authorised officer may, at any reasonable time (by force if necessary), enter premises in which there has been a fire for the purpose of investigating what caused the fire; or why it progressed as it did. If an authorised officer exercises this power of entry, he may: take onto the premises any other persons, and any equipment, that he considers necessary, inspect and copy any documents or records on the premises or remove them from the premises, carry out any inspections, measurements and tests in relation to the premises or an article or substance found on the premises, that he considers necessary, take samples of an article or substance found on the premises (but not so as to destroy it or damage it unless it is necessary to do so for the purpose of the investigation), dismantle an article found on the premises (but not so as to destroy it or damage it unless it is necessary to do so for the purpose of the investigation), take possession of an article or substance found on the premises and retain it for as long as is necessary for the purpose of: examining it and doing anything he has power to do under the paragraphs above, ensuring that it is not tampered with before his examination of it is completed, or ensuring that it is available for use as evidence in proceedings for an offence relevant to the investigation, and require a person present on the premises