Motorists who use the M27 and M3 are being warned not to fall for a long-standing motorway speeding myth that could prove costly.
Experts say many drivers think smart motorway speed cameras are only active at certain times, potentially leading them to exceed the limit.
If you are caught speeding, you can expect hefty fines, penalty points and even disqualification from driving.
Graham Conway, a motoring specialist from vehicle leasing firm Select Car Leasing, said motorway cameras can enforce speed limits at any time, even when no variable limit is displayed.
Mr Conway said: "We hear this quite often, but it’s something that could potentially ruin your day if you get it wrong.
"It appears that many motorists think the speed cameras on smart motorways are only in operation when the matrix signs on the gantries show a variable speed limit, say 50mph or 60mph.
"They are aware that they need to slow down when they see this, but wrongly believe that at other times they won’t get clocked breaking the speed limit, as long as they don’t encounter the police.
"This simply is not right.
"Online motoring forums are full of accounts from drivers who’ve been caught out in such a manner.
"And the penalties for breaking the speed limit on a motorway can be severe."
Standard motorway cameras, including those on gantries, can still catch drivers exceeding 70mph even when no lower speed is being displayed.
What speed actually triggers a camera?
Contrary to popular belief, there is no legally guaranteed "10% plus 2mph" tolerance when it comes to speed enforcement.
Experts from BigWantsYourCar.com explained: "The idea that you’re safe doing 35mph in a 30 zone is one of the biggest myths we hear.
"Technically, you’re liable for a fine the moment you go even 1mph over the limit."
While the National Police Chiefs’ Council (NPCC) does recommend a "10% plus 2" margin to allow for officer discretion, this is not a legal threshold and can vary depending on the enforcement area or the officer reviewing the case.
RAC advice adds: “The law states that you are liable for a speeding fine as soon as you exceed the limit, so if you’re doing 31mph in a 30 limit or 71mph on a motorway, you’re breaking the law and could receive a fine.
“It is well worth remembering this is totally dependent on the officer who catches the speeder, and it is up to that officer whether to fine the offender or not.
“The best advice is to not speed full stop.”
Why is the M3 Junction 9 entry slip road shut until November 2027?
Outside of speed camera myths to be aware of, drivers on the M3 are facing a diversion until November 2027 due to long-standing roadworks.
The closure of the northbound Junction 9 entry slip road forms part of National Highways' £280 million project to reconstruct the junction and improve links between the M3 and A34.
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During the closure, drivers aiming to travel northbound will need to head south to Junction 11 at Hockley Cross Interchange, before leaving and rejoining the northbound carriageway.
National Highways has advised against relying on satnavs for the diversion, warning that they may direct vehicles onto closed or unsuitable routes.
National Highways expects the improvement scheme to be completed by 2028, with peak-time journeys through the junction towards the A272 expected to be nearly 30% faster.
Did you know about this speed camera myth? Let us know in the comments.
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