Please note this extract from the Department of Transport legislation (quotation in green italics):
Great Britain uses imperial units for speed measurement. The law requires that speedometers must include a miles-per-hour display. Please note in particular that any modified display must be visible in daylight and in darkness.
Markings may be added to the existing speedometer provided they are:
- can be seen clearly in daylight and when the instrument is lit during darkness.
kilometres per hour, either simultaneously, or by operation of a switch.
Note: We can not accept secondary devices, hand written changes or multiple stickers applied to the
speedometer. We can only accept the changes detailed below.
The speedometer must be marked up to the maximum speed of the vehicle, with graduations at 1, 2, 5, or
10mph, and with values at intervals not exceeding 20mph. For this change we can accept the following
a) That the factory fitted speedometer is dual marked as standard
b) The existing (digital) speedometer is, permanently, re-programmed, through a standard feature of the
vehicle, to display the vehicle speed in mph
c) A miles per hour speedometer is fitted in-place of the factory fitted unit
d) A professional, single, miles per hour, overlay is applied directly to the speedometer face plate, not the
glass front plate (the overlay must be durable and accurate, with markings visible in both day and night
e) A dual marked dial / facia has been added as a replacement to the factory fitted one