KPH Speedometers - Edwin
Can anyone clarify the law on driving a car with a KPH only speedometer?
Is it illegal to drive such a car on UK roads? Or will it only be a problem when the MOT is due?
KPH Speedometers - jeds
According to BBC Watchdog guide to importing new cars from Europe, Speedo's must display speed in MPH

See: www.bbc.co.uk/watchdog/guides_to/importinganewcar
KPH Speedometers - Marcus
It used to be OK to 'locally' modify the display by marking the speedo glass with crayon or similar. Assuming you don't have a digital display.
KPH Speedometers - Dwight Van Driver
Motor Vehicles (Con & Use) Regs, 1986 Reg 35

Motor Vehicle shall be fitted with a speedometer which, if the vehicle was first used on or after 1.4.1984, shall be capable of indicating speed in BOTH miles per hour and kilometers per hour, either simultaneously or, by the operation of a switch seperately
Except, vehicles masx speed not exceeding 25 mph, motor cycle n e 100 cc, invalid carriage, fitted with tacho, etc, etc.(does not include any vehicle driven by Toad)

DVD
KPH Speedometers - John Davis
Edwin. DVD has clarified this very well and, to add my bit of information, my imported vehicle (1990 model)has the main speed register in KPH and the secondary as MPH and I have had no problems with MOT and have been told that this is acceptable.
However, because of the need nowadays to be more observant of speeds, I have put a secondary perspex "dial" over the speedo display, and have marked it in MPH. This has never been queried at MOT time.
KPH Speedometers - CMark {P}
In January 2001, I personally imported a 1994 Mercedes G-wagon (bought used in Germany) with a kph-only speedo. The car has since passed 3 MOTs (at 2 different MOT stations) without even a comment made about the lack of MPH markings.