It's an urban myth that drivers are legally entitled to stray over the speed limit.

Yes, the police are issued guidelines that allows them to give leeway of up to 10 per cent plus 2mph to account for inaccuracies of speedometers, but there is no actual legislation that says drivers are legally entitled to do this. I've met lots of drivers over the years who have been prosecuted for being a few miles over and it's important to note that speed limits are there for a reason and should not be treated as vague targets.

It ultimately comes down to the discretion of the local police force. Some officers might overlook a car that's doing 78mph on the motorway or 34mph in a 30mph area. Some will not. It will very much depend on the location and time of day. I've met drivers who have taken their cases to court because they wrongly believed there was a law in place that allowed them to drive 10 per cent + two miles over the limit. They all lost and received heavy fines.