48—(1) A constable in uniform or, if accompanied by such a constable, an inspector may stop and detain a vehicle for the purpose of entering and searching it in the exercise of a power conferred—
(a)by section 18(1), or
(b)by a warrant under section 18(4) or 22(1).
(2) A constable in uniform may stop and detain a vehicle for the purpose of entering and searching it in the exercise of a power conferred—
(a)by section 21(2), or
(b)by a warrant under section 21(4).
(3) If accompanied by a constable in uniform, an inspector may stop and detain a vehicle for the purpose of entering it and carrying out an inspection in the exercise of a power conferred—
(a)by section 24(2), 25(2), 26(2), 27(2) or 28(2), or
(b)by a warrant under section 26(4) or 27(4).
(4) A vehicle may be detained for as long as is reasonably required to permit a search or inspection to be carried out (including the exercise of any related power under this Act) either at the place where the vehicle was first detained or nearby.