(7A) 9[ Notwithstanding anything contained' in subsection (7), any person, who has a valid driving licence granted before the commencement of the Motor Vehicles (Amendment) Act, 1978 , authorising him to drive a heavy motor vehicle or, as the case may be, a medium motor vehicle, shall, for the period specified in such licence, be Permitted to drive-
(a) any heavy goods vehicle, heavy passenger motor vehicle, medium goods vehicle, medium passenger motor vehicle, or light motor vehicle, where the licence is for driving any heavy motor vehicle;
(b) any medium goods vehicle, medium passenger motor vehicle, or light motor vehicle, where the licence is for driving any medium motor vehicle.]