Motorists who fail to declare who was behind the wheel when a speeding offence was committed are to face stiffer penalties from Monday.
Most speeding vehicles are caught by speed cameras
Those convicted of failing to provide information on the identity of a driver will get six penalty points on their licence - doubling the current rate.
The aim is to punish those who falsely claim they do not know who was driving.
Ministers say those with good reason for not naming a driver, such as if a vehicle is stolen, will have a defence.
According to the Department of Transport, relatively few speeding motorists are pulled over on the spot.
Most vehicles committing offences are caught by speed cameras, which cannot always identify the driver.
The government says it is concerned that some motorists are exploiting the so-called "Hamilton defence", named after former Conservative MP Neil Hamilton and his wife, Christine, who avoided a speeding fine four years ago.
They said they had been taking it in turns behind the wheel so could not say which of them had been flashed by the camera.
Vehicle owners are obliged under the Road Traffic Offenders Act 1988 to tell police who was driving at the time of an alleged motoring offence.
Critics said those who genuinely did not know who was driving their car when an offence was committed could suffer.
Sheila Rainger, of the RAC Foundation, said: "It's a provision that has been abused and that's really the reason behind upping the stakes in this way.
"Our concern is that it will cause hardship to that small number of motorists who genuinely do not know.
"You might say 'how on earth can you not know who is driving your car' but for a family car shared between four or five members of the one family it's quite possible you genuinely may not know."
Lawyer Nick Freeman - known as Mr Loophole because of his success at getting clients acquitted of motoring offences - said he also thought the new legislation unfair.
He said: "I'm concerned that people are going to be placed under pressure to try and name - and of course there are genuine cases; many, many genuine cases where people simply don't know who was driving, and my theory is that they're going to put down a name simply to avoid getting six penalty points."