Over speeds and roadside fines

Sand Fisher:
Overspeeds are classed as C&U offences.

At the risk of sounding stupid what are C & U offences? Having been pulled by DVSA plenty of times in both UK and Irish registered lorries not once has anyone ever mentioned overspeeds despite there plenty for them to see, As I said before the only people who take any notice of them are office people with nothing better to do.