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UK speed camera tolerances revealed: is your car’s speedo accurate?

Hugo Griffiths 2019-04-24 (All day)

We investigate the internet rumors surrounding UK speed camera tolerances and whether your car speedo can be trusted

At the start of 2019, rumours swept the internet that speed camera tolerances on certain motorways were so strict, they would issue tickets if drivers exceeded the 70mph limit by just 1mph.

Those stories turned out to be untrue and unfounded. But rather than allow misinformation about speed camera ‘thresholds’ to circulate unchecked, Auto Express asked the UK’s 45 police forces via Freedom of Information requests how strictly their 3,224 speed cameras enforce limits.

UK speed cameras explained

The majority of the forces that responded said their cameras would only activate when drivers exceed the speed limit by 10 per cent plus 2mph, in line with prosecution guidelines from the Association of Chief Police Officers.

This means cameras won’t issue tickets until someone is driving at 35mph or more in a 30mph limit, or 79mph or more on the motorway, for example.

The Metropolitan Police, which uses a less strict, 10 per cent plus 3mph threshold, say this is “a proportional response to the high volumes of traffic” in the capital. Lancashire Police also sets its cameras so that they activate at 10 per cent plus 3mph, and says that this has been done “to ensure greater tolerance or discretion”.

A number of forces wouldn’t tell us their camera thresholds, arguing that knowledge of these would encourage drivers to speed. All police forces that told us their thresholds said these applied to both fixed and average speed cameras.

Speed camera thresholds across the UK

Police force

Number of cameras

Camera activation threshold

Avon and Somerset 41 10% + 2mph
Bedfordshire 38 Would not reveal threshold
Cambridgeshire 32 Would not reveal threshold
Cheshire 15 10% + 2mph
Cleveland 4 10% + 2mph
Derbyshire 18 10% + 2mph
Devon and Cornwall 98 10% + 2mph
Durham 0 fixed 10% + 2mph
Essex 63 Don't use a standard threshold
Greater Manchester 235 Would not reveal threshold
Gwent 21 10% + 2mph
Hampshire 36 10% + 2mph
Hertfordshire 53 Would not reveal threshold
Kent 109 10% + 2mph
Lancashire 34 10% + 3mph
Leicestershire 30 10% + 2mph
Merseyside 18 10% + 2mph
Metropolitan Police/TfL 805 10% + 3mph
Norfolk 26 10% + 2mph
North Wales 28 10% + 2mph
Northumbria 55 10% + 2mph
Nottinghamshire 48 Refused to confirm if threshold exists
Police Service of Northern Ireland 12 10% + 2mph
Scotland 173 Refused to confirm if threshold exists
South Wales 137 10% + 2mph
South Yorkshire 25 10% + 2mph
Staffordshire 286 Would not reveal threshold
Suffolk 4 10% + 2mph
Thames Valley 294 10% + 2mph
Warwickshire 28 10% + 2mph
West Mercia 23 10% + 2mph
West Midlands 33 Would not reveal threshold
West Yorkshire 402 10% + 2mph

Can you trust your car speedo?

In addition to asking police how strictly their speed cameras enforce limits, we investigated how accurate the speedometers on 10 cars were. We did this by comparing how fast they said we were going with our actual speed, revealed by a VBox meter.

Car speedometers are not allowed to ‘under-read’ – they can’t tell you you’re going more slowly than you really are – but they are allowed to over-read by up to 10 per cent plus 6.25mph. So they could read 50.25mph at 40mph.

All the cars we assessed were well within legal limits, although some read with near-perfect accuracy, while others over-read by 3mph. This, with the different approaches police have to enforcing limits, means some variance will always remain around speeding.

Commenting on our investigation, AA president Edmund King said it is “sensible to have some flexibility” with speed-limit enforcement, “as the last thing we need is drivers concentrating solely on the speedo and not the road”.

King added that, with speedometers becoming increasingly accurate, “Auto Express’s testing is a valid reminder to drivers not to gamble on their speedo perhaps providing some leeway”.

UK speeding fines and how to appeal them

Our speedo accuracy test explained

The VBox is a clever piece of kit that uses a GPS signal to measure a car’s speed. It’s very accurate, gauging velocity to within 0.1km/h, so is perfect for assessing speedos.

We set our test cars to 30, 50, 60 and 70mph using the built-in speed limiter or cruise control to ensure a steady speed, then used the VBox to measure how fast we were going. This gave us a fair idea of the discrepancy between actual and indicated speed.

“Not many drivers have access to a VBox, but a separate smartphone app or sat-nav can give you an idea of how accurate your speedo is.


True speed at indicated 30mph

True speed at indicated 50mph

True speed at indicated 60mph

True speed at indicated 70mph

Kia e-Niro First Edition 27mph 47mph 57mph 67mph
BMW i3s 28mph 48mph 58mph 68mph
SEAT Arona 1.0 TSI 115 29mph 49mph 60mph 69mph
SEAT Tarraco 2.0 TDI 150 manual 29mph 49mph 59mph 68mph
Skoda Kodiaq 2.0 TDI 150 manual 28mph 48mph 57mph 67mph
Peugeot 5008 BlueHDi 130 manual 28mph 48mph 57mph 68mph
Volvo XC40 D4 auto R-Design 30mph 49mph 59mph 69mph
Mazda MX-5 2.0 27mph 48mph 58mph 68mph
Dacia Duster dCi 115 28mph 48mph 58mph 68mph
BMW 330i M Sport 28mph 48mph 57mph 67mph

Do you think that UK speed camera tolerances are too strict? Let us know in the comments below…

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