Speed cameras and their tolerance levels, how fast do you have to be travelling before they are triggered?

We’ve all been there, travelling down any given road at what we believe to be the correct speed limit, not realising that our speed may have crept up by a mile per hour or two, and then we see the flash from a speed camera in our rear-view mirror. We then wait nervously for a couple of weeks to see if a fixed penalty notice arrives on our doorstep.

But what is the speed camera threshold? At what point does a camera get triggered?

The answer is, they all vary; different police authorites have different thresholds.

The first thing that drivers must be aware of is that any given police authority will apply guidelines and thresholds at their discretion. The golden rule of thumb is of course not to break the law by committing a speeding offence.

With figures collated by Auto Express, who contacted all of the UK’s 45 police authorities via Freedom of Information requests, the thresholds attributed to some of the 3,224 speed cameras across the country were revealed.

34 police authorities across the UK disclosed information pertaining to their speed camera activation thresholds, with the majority triggering at 10% plus 2mph.

Therefore at 30mph a camera may be triggered at 35mph, 40mph could see a camera triggered at 46mph, and at 70mph that threshold could increase to 79mph.

There are a number of police authorities where the threshold varies, such as the Metropolitan Police Authority where a camera may trigger at 10% plus 3mph.

Some authorities refused to disclose if they operated a threshold, citing that knowledge of this information could encourage drivers to speed.

The threshold, or buffer zone, exists so as to help prevent drivers from concentrating on their speedometer rather than the road.

A vehicle’s speedometer is not 100% accurate, in some cases they are allowed to over-read a car’s speed by as much as 10%. However, a vehicle’s speedometer is not allowed to under-read.

The police authorities which operate a 10% plus 2mph are:

Avon and Somerset




Devon and Cornwall








North Wales


Northern Ireland

South Wales

South Yorkshire


Thames Valley


West Mercia

West Yorkshire

The police authorites which operate a 10 plus 3mph threshold are Lancashire and the Metropolitan Police.

The remaining authorities did not disclose whether they operated a threshold or not.