6.—(1) A traffic authority may, pursuant to section 65(1) of the 1984 Act, cause or permit the placing of the portable light signals if and only if—
(a)permission is given in writing, or in a case of urgency, given orally and confirmed in writing as soon as reasonably practicable thereafter; and
(b)either—
(i)the written permission of the authority includes express approval to the placing of the signals at a particular site; or
(ii)the authority is satisfied that the circumstances of the particular case fall within one of the sets of circumstances specified in sub-paragraph (2).
(2) The sets of circumstances referred to in sub-paragraph (1)(b)(ii) are—
(a)where the signals are to be operated and maintained by, and are under the regular supervision of, a constable in uniform during the progress of a temporary scheme of traffic control;
(b)where the signals are placed on a length of road along which—
(i)there is no junction carrying vehicular traffic to or from it; and
(ii)the width of the carriageway is temporarily restricted so as to carry only one line of traffic;
(c)where the signals are placed at a level crossing when work in relation to that crossing is being carried out;
(d)where the signals are placed on a road which is—
(i)adjacent to the temporary site of road, building or engineering works; and
(ii)is used for the movement of vehicles, materials, plant or equipment into and out of the site of the works.
(3) Nothing in this direction is to be taken to limit or affect the powers of a constable or the chief officer of police under section 67(1) of the 1984 Act (placing of temporary signs on roads in extraordinary circumstances).