In the UK they recognise that, since a speedometer is not required by law, they cannot charge you for exceeding the speed limit since they must show intent to exceed something you are not able to measure - seems more logical to me.

However, they can still get you for "furious and reckless riding", often because you are going faster than is reasonable for the conditions. This charge was used in the early days of cycling and was taken from an existing law applying to horsriders (serious shortge of speedometers in the 19th C.