Crackdown on Beach Speeders

During the driving test you're supposed to demonstrate that you can stay safely within the speed limit whilst being aware of your surroundings. Would a device limiting your car to the area's speed limit make it easier ?

Re Cycling and speed limits - how can it be enforced when it's not compulsory to have a computer on your bike ?

If you can't trust yourself to drive responsibly, you shouldn't be driving a car. If you rely on a device to drive responsibly, you shouldn't be driving a car. Get a bus/tube/taxi instead.