11.—(1) The authorisation requirements applicable to Part 2 vehicles or Part 2 vehicle-combinations are—
(a)as respects any vehicle or vehicle-combination falling within Schedule 1, 2, 3 or 4, the requirements specified in the Schedule in question; and
(b)as respects all such vehicles or vehicle-combinations, the requirements specified in articles 12 to 18.
(2) But the requirements specified in articles 12 to 17 do not apply to a mobile crane or road recovery vehicle in any case where—
(a)a civil emergency or road traffic accident has occurred;
(b)as a result, there is a danger to the public;
(c)the owner or user of the crane or vehicle has received a request made by the police for the vehicle to be used for the purposes of immediate clearance of an area affected by the emergency or accident;
(d)the crane or vehicle is used on roads within 24 hours of receipt of the request; and
(e)it is not reasonably practicable to comply with the requirements of those articles.
(3) Nothing in this article prevents a motor vehicle which falls within the definition of a mobile crane in paragraph 2 of Schedule 2, but which does not comply in all respects with the authorisation requirements for mobile cranes specified in that Schedule, from complying instead with the authorisation requirements for engineering plant specified in Schedule 3 provided that the motor vehicle in question also falls within the definition of engineering plant in paragraph 2 of that Schedule.
(4) For the purposes of this Order, a motor vehicle that complies with the authorisation requirements for engineering plant in the manner described in paragraph (3) is to be treated as engineering plant.