4. The conditions in accordance with which an invalid carriage must be used, in order that the modifications of the statutory provisions mentioned in subsection (1) of section 20 of the 1970 Act shall have effect in the case of the invalid carriage (being modifications of certain statutory provisions which relate to the use of vehicles on footways and roads) shall be—
(a)in the case of Class 1, Class 2 and Class 3 invalid carriages that the invalid carriage must be used—
(i)by a person falling within a class of persons for whose use it was constructed or adapted, being a person suffering from some physical defect or physical disability;
(ii)by some other person for the purposes only of taking the invalid carriage to or bringing it away from any place where work of maintenance or repair is to be or has been carried out to the invalid carriage;
(iii)by a manufacturer for the purposes only of testing or demonstrating the invalid carriage;
(iv)by a person offering to sell the invalid carriage for the purpose only of demonstrating it; or
(v)by a person giving practical training in the use of the invalid carriage for that purpose only;
(b)in the case of Class 1, Class 2 and Class 3 invalid carriages, that any horn fitted to it must not be sounded in the circumstances set out in regulation 5;
(c)in the case of Class 3 invalid carriages only—
(i)that the invalid carriage must not be used by a person who is aged under 14 years;
(ii)that, when being used on a footway, the invalid carriage must not be driven at a speed greater than 4 miles per hour;
(iii)that the invalid carriage must not be used on a footway unless the device fitted in accordance with regulation 10(1)(a) is operating; and
(iv)that the invalid carriage must not be used at any time unless the speed indicator fitted to it in accordance with regulation 10(1)(b) is operating.