12.—(1) Subject to the following paragraphs of this regulation, an enclosed vehicle and any enclosed part of a vehicle is smoke-free if it is used—
(a)by members of the public or a section of the public (whether or not for reward or hire); or
(b)in the course of paid or voluntary work by more than one person (even if those persons use the vehicle at different times, or only intermittently).
(2) A vehicle or part of a vehicle is enclosed for the purposes of paragraph (1) where it is enclosed wholly or partly by a roof and by any door or window that may be opened.
(3) Except where paragraph (4) applies, “roof” in paragraph (2) includes any fixed or moveable structure or device which is capable of covering all or part of the vehicle, including any canvas, fabric or other covering.
(4) In relation to a vehicle that is engaged in conveying persons, “roof” does not include any fixed or moveable structure or device which is completely stowed away so that it does not cover all or any part of the vehicle.
(5) A vehicle is not used in the course of paid or voluntary work for the purposes of paragraph (1) (b) where it is used primarily for the private purposes of a person who—
(a)owns it; or
(b)has a right to use it which is not restricted to a particular journey.