The guidelines are just that, Guidelines. Some areas are "zero tolerance" so in theory you'd get done for 71.
There is no national hard and fast rule other than the actual speed limit itself, what speed you get done at over that is up to the policy set by the areas chief constable or the officer who pulls you that day...........if his/her moning bacon butty was not to his/her liking or their hair didn't look good on last nights police, camera action prog. you can be in trouble at just 1mph over.
Follow Andy B's advice and don't go over the limit at all or try not to get caught.......tough choice
Ray.