35—Rear vision mirrors—surfaces
(1) A rear vision mirror required to be fitted to the side of a motor vehicle with a GVM over 3.5 tonnes must have a reflecting surface of at least 150 square centimetres.
(2) The reflecting surface of the rear vision mirrors that are required to be fitted to a motor bike or moped must—
(a) each be of the same curvature; and
(b) if convex, be part of a notional sphere with a radius of at least 1.2 metres.