just buy one of those conversion kits for 20 quid that jump the speed signal off the ecu and make your existing clocks in mph, and limit the car to 210mph, job done
I cut the speed signal wire going into my ecu yesterday.
Took roughly 2 seconds... bye bye speed limiter
Apparently you shouldn't do that, can't remember why
I got one of those mph converter things off ebay for about 20 quid, instructions had two wires round the wrong way but it was pretty obvious and easy to fit