Regulation 204 applies. As long as the driver’s view is not obstructed a chip is not illegal. It is only when it affects the visibility that it becomes an unroadworthy vehicle.
Driving view to be unobstructed
Reg 204. (1) No person shall operate on a public road a motor vehicle-
(a) which is not so constructed and maintained as to afford the driver thereof a full and clear view of the roadway ahead and to his or her right and left when the vehicle is in use;
(b) which is not fitted with a rear-view mirror or mirrors enabling the driver of such vehicle, when he or she is in the driving position, to see in clear weather a clear reflection of traffic to the rear: Provided that the provisions of this paragraph shall not apply in respect of a tractor;
(c) which is a motor car, minibus, bus or goods vehicle, the gross vehicle mass of which does not exceed 3 500 kilograms and which, according to the registration certificate thereof, was registered for the first time on or after 1 January 1987, unless it is fitted with an exterior rear-view mirror on the driving side and an interior rear-view mirror: Provided that where the interior rear-view mirror does not enable the driver, when he or she is in the driving position, to see in clear weather, a clear reflection of traffic to the rear, an additional exterior rear-view mirror shall be fitted on the side opposite to the driving seat and in such a case it shall not be necessary to fit an interior rear-view mirror;
(d) which is a mini-bus, bus or goods vehicle, the gross vehicle mass of which exceeds 3 500 kilograms and which, according to the registration certificate thereof, was registered for the first time on or after 1 January 1987, unless it is fitted with an exterior rear-view mirror on the driving side and an exterior rear-view mirror on the side opposite to the driving seat; or
(e) which is a motor cycle, a motor tricycle or motor quadrucycle unless it is fitted with a rear-view mirror on the right side of the handlebars thereof, and such cycle shall also be fitted with a rear-view mirror on the left side of its handlebars.
(2) Every rear-view mirror of a motor vehicle-
(a) which-
(i) is a motor car, minibus, bus or goods vehicle, the gross vehicle mass of which does not exceed 3 500 kilograms and which, according to the registration certificate thereof, was registered for the first time on or after 1 January 1976; or
(ii) is a minibus, bus or a goods vehicle, the gross vehicle mass of which exceeds 3 500 kilograms and which, according to the registration certificate thereof, was registered for the first time during the period 1 January 1976 to 31 December 1986,
shall be either flat or spherically convex and have an average radius of curvature of not less than one comma two metres; or
(b) contemplated in subregulation (1)(d) shall be either flat or spherically convex and have an average radius or curvature of not less than one comma eight metres.
Also view:
Road Safety and Your Windscreen
Chip Repair and Windscreen Safety
