The Motor Vehicles (Approval) Regulations 2001

4.  Each rear view mirror fitted to the vehicle shall either—

(a) comply with the requirements (including marking requirements) of Annex II to Directive 71/127/EEC as last amended by Directive 88/321/EEC or of Part I of ECE Regulation 46.01 for a Class I mirror in the case of an interior mirror and a Class III or a Class II mirror in the case of an exterior mirror; or

(b) comply with the dimension requirements and the following requirements—

(i) the edge of the reflective surface shall be enclosed within a protective housing;

(ii) all parts of the external surface of the mirror which are, in the case of an interior mirror, contactable by a sphere of 165 mm diameter, and in the case of an exterior mirror, by a sphere of 100 mm diameter, shall have a radius of curvature of not less than 2.5 mm, with the exception of fixing holes or recesses less than 12 mm wide if these are blunted;

(iii) exterior mirrors shall be capable of rotating inwards towards the vehicle when a force of 10 kg is applied horizontally at the extreme outer edge in a longitudinal plane from both the front and the rear. The axis of rotation shall lie within 50 mm of the surface at which the mirror is attached to the vehicle bodywork.