The general rule allowed by police forces on British roads is 10% over speed limit + 3 MPH, so a 70 limit road would be a maximum of 80 MPH before the police would bother to issue a penalty, anything less is not worth the time with paper work as it would most likely be disregarded by the CPS.
If you are stopped by a traffic officer then the he / she may see fit just to issue you with a friendly warning especially if it is your first offence, remember they will treat you as you treat them so play nice.
Over the “maximum limit” would be considered speeding and / or driving with undue care and attention, either of which could lead to points on your licence and fine, if you are caught doing 100 MPH or over then it is almost certainly an instant driving ban through the courts and could also carry sentence.
Of course all these rules are dismissed if your driving is considered to be dangerous or reckless.
Personally I have passed camera vans speeding and never received any notice, I suppose it depends on if their equiptment is monitoring you at that moment and if it is correctly aligned and calibrated.
If you do ever receive a notice of speeding and you are 100% sure you were not then challenge it, there have been several cases where hand held lasers have been used wrong producing false results.