29(1)A police officer of at least the rank of superintendent may apply to a judicial authority for the issue of a warrant of further detention under this Part.
(2)A warrant of further detention—
(a)shall authorise the further detention under section 41 of a specified person for a specified period, and
(b)shall state the time at which it is issued.
(3)The specified period in relation to a person shall end not later than the end of the period of seven days beginning—
(a)with the time of his arrest under section 41, or
(b)if he was being detained under Schedule 7 when he was arrested under section 41, with the time when his examination under that Schedule began.
(4)In this Part “judicial authority” means—
(a)in England and Wales, the Senior District Judge (Chief Magistrate) or his deputy, or a District Judge (Magistrates' Courts) who is designated for the purpose of this Part by the Lord Chancellor,
(b)in Scotland, the sheriff, and
(c)in Northern Ireland, a county court judge, or a resident magistrate who is designated for the purpose of this Part by the Lord Chancellor.