Basic thing is that speedos in the UK had a tolerance limit of plus or minus 10% at an indicated 30 MPH. So at an indicated 30 you could be doing anything from 27 to 33, this depended on tyre wear. This goes back to when there was only one speed limit of 30 MPH in built up areas, everywhere else it was unrestricted. In 1999 the EU introduced a rule that said that no speedo could indicate less than actual. So at any indicated speed you could be doing below indicated but never above indicated. This was introduced in the UK from 2001. However vehicles built before 2001 are still subject to the plus or minus 10% rule. That is why speed cameras are set the way they are to allow for this. Jobsworths with speed guns are doing people for 31 in a 30 zone, perfectly correct if a little harsh, for vehicles made 2001 and on, but not legal for vehicles made before that date that have the plus or minus 10% allowance. Because providing the indicated speed is 30 MPH they cannot be legally prosecuted until they exceed 33 MPH. I know it's a mute point but there are lots of people taking points and awareness courses when they legally have no need to, because they have done technically nothing wrong. It's a bit of a scam really, police must be aware of it but the majority of Joe public are not, it's a money spinner so the police say nothing.
personal choice, as it was when the car was built
