andysh: Also isn't it 10% ontop of the speed limit when tickets start coming?
A threshold of intolerance has been set at speeds in excess of 10kmh above the speed limit. That translates to 111kmh+ on the open road and 61kmh+ in most urban settings. I understand the tolerance to be zero around schools/school buses.
In reality you could be ticketed for travelling at just 1kmh over the speed limit, but that's fairly unlikely to happen.

The whole detector/jammer issues always amuses me. What a waste of money - don't speed.