(3) A driver shall overtake on the right and shall not move in towards the left until it is safe to do so.
(4) Notwithstanding paragraph (3) of this bye-law, a driver may overtake on the left—
(a) where the driver of the vehicle about to be overtaken has signalled his intention to turn to the right and the driver of the overtaking vehicle intends, after having overtaken, to go straight ahead or to turn to the left,
(b) where the driver of the overtaking vehicle intends, after having overtaken, to turn left at a road junction and has signalled this intention,
(c) in slow-moving traffic, when vehicles in the traffic lane on the driver's right are moving more slowly than the overtaking vehicle.