I'm more than sure.

Here's what ACPO say on the matter.

Driving at any speed over the limit is an offence. The differing speed limits are generally related, and proportionate, to the risks to all road users using that road. Where police officers consider that an offence has been committed i.e. that a motorist has driven at any speed over the relevant speed limit, they should consider whether it is appropriate to take enforcement action against the offender.

The Police Service now uses technology that enables it to prove that an offence has been committed as soon as a driver exceeds the relevant speed limit by a very small margin. Motorists will therefore be at risk of prosecution immediately they exceed any legal speed limit.

The guidance to police officers is that it is anticipated that, other than in the most exceptional circumstances, the issue of fixed penalty notices and summonses is likely to be the minimum appropriate enforcement action as soon as the following speeds have been reached.........

They then quote a 10% + 2 table.

But note how it is guidance, it can be varied. Do 31 mph outside a school when kids are about and see what happens!

And also note it is police guidance. The speed camara partnerships aren't police and the guidance does not necessarily apply. No partnership (as of the last time I heard it on the news about a year ago) had published their limits and they were actively against publication as it may encourage driving at these limits, not the legal ones.

Posted By: Johnny Comecardiff, May 2, 13:05:08