im pritty certain thats its up to the individual police force what they set them too. The guidence was 10% plus 1 mph. But i think they can do you for 31mph in a 30 etc if they wish.

Also what calibrated devices did you have setup to calculate your speeds when you say you were doing 31-32? speedos are not exactly accurate in most cases. and nor are your average gps imo fo course.