Two-fifths of drivers are unaware they face tougher punishments for using a hand-held mobile phone while driving, a study has found.
Some 39% do not know that penalty points and fines will double to six and £200 respectively from Wednesday, according to a Co-op Insurance poll of 1,500 UK drivers conducted last week.
The firm described the findings as "very worrying".
Drivers can be banned from Britain's roads if they receive 12 points within three years, while new drivers can have their licence revoked if they get six points within two years of passing their test.
Stricter penalties for illegal phone use are being introduced by the Department for Transport following a series of high-profile cases and research suggesting the practice is widespread.
Twenty-two people were killed and 99 seriously injured in accidents on Britain's roads in 2015 where a motorist using a mobile was a contributory factor, latest figures show.
In October, lorry driver Tomasz Kroker was jailed for 10 years after killing a woman and three children by ploughing into their stationary car on the A34 near Newbury, Berkshire, while distracted by his phone.
Motoring groups believe a sharp decline in the number of drivers caught using a hand-held phone is partly due to police budget cuts affecting enforcement.
Home Office data shows just 16,900 drivers were handed fixed penalty notices for illegally using a phone in England and Wales in 2015, compared with 123,100 in 2011.
But there was also a 27% fall in the number of full-time dedicated roads policing officers, excluding London, between 2010 and 2015, according to RAC analysis.
The Co-op Insurance survey found that almost a third (30%) of drivers admit to using their phone behind the wheel and over half (54%) do not believe the tougher punishments being introduced this week will deter offenders.
James Hillon, head of products at Co-op Insurance, told the Press Association: "We welcome the penalty changes as anything which helps make our roads safer can only be a good thing.
"However, it is very worrying that a significant proportion of drivers are unaware of the changes given how significant they are.
"Whilst it seems as though the increase in penalties may encourage better behaviour, with a quarter now less likely to phone and drive, much of the driving population believe that the increase could have gone further."
Jayne Willetts, lead for roads policing for the Police Federation of England and Wales, also welcomed the introduction of harsher punishments but called for all mobile use to be banned, even if it does not involve holding a device.
She said: "The wider issue of distraction should be addressed - the distraction of connecting to hands free, dialling a number. Legislation must be clear on this."
AA president Edmund King said: "We must stop this epidemic of texting/tweeting drivers by changing attitudes, and the campaign that kicks off this week is a big step in the right direction."
A Department for Transport spokesman said: "It is unacceptable to use a handheld mobile phone while driving for any purpose.
"A hard-hitting Think! campaign will launch on Wednesday when the tough new penalties come into force. This will not only highlight the dangers of using a phone at the wheel but also the increase in penalties."