107.—(1) Save as provided in paragraph (2), no person shall leave, or cause or permit to be left, on a road a motor vehicle which is not attended by a person licensed to drive it unless the engine is stopped and any parking brake with which the vehicle is required to be equipped is effectively set.
(2) The requirement specified in paragraph (1) as to the stopping of the engine shall not apply in respect of a vehicle—
(a) being used for ambulance, fire brigade or police purposes; or
(b) in such a position and condition as not to be likely to endanger any person or property and engaged in an operation which requires its engine to be used to—
(i) drive machinery forming part of, or mounted on, the vehicle and used for purposes other than driving the vehicle; or
(ii) maintain the electrical power of the batteries of the vehicle at a level required for driving that machinery or apparatus.
(3) In this regulation “parking brake” means