A ban on using handheld mobile phones while driving has come into force.
Drivers could be given a £30 on-the-spot fine
The minimum fine for breaking the law is £30, but police are expected to be lenient with offenders - at least for the first two months.
Hands-free kits are allowed, but many road safety experts say they do not reduce the risks of having an accident.
Despite the changes a survey of drivers found 94% were unaware of the changes - even though a quarter admitted phoning or texting while behind the wheel.
Police forces can issue on-the-spot fines from Monday, but the Association of Chief Police Officers has recommended that officers in England and Wales give drivers a period of grace to get used to the new laws.
WHAT ARE THE NEW RULES?
Apply from 1 December
New offence of "using a hand-held phone while driving"
£30 fixed penalty fine
Rising to up to £1,000 if the matter goes to court
Rising to up to £2,500 for drivers of vans, buses, coaches and lorries
Drivers in Scotland, however, have been given no such concession.
Offending motorists south of the border can expect verbal warnings until February in order to "assist in the education of drivers".
But police will still be able to hand out instant fines if they feel a driver's use of a mobile phone poses a serious risk, or if their use contributes to a collision.
And road safety minister David Jamieson said that while the new ban applies only to hand-held mobile phones "police can use other powers to prosecute a driver if they are distracted by a call on a hands-free phone".
Road safety charity Brake fears some phone companies will exploit the ban to promote their hands-free models.
Calling for a ban on the use of all phones by drivers, its chief executive, Mary Williams said: "The use of hands-free kits while driving may not be illegal yet, but they certainly do not make driving any safer."
The Royal Society for the Prevention of Accidents said: "At least 20 people have died on Britain's roads in crashes where mobile phones have been implicated."
The AA Motoring Trust said drivers using mobiles were four times more likely to have an accident even if they were employing hands-free devices.
But Mr Jamieson said a ban on hands-free devices would be extremely difficult to enforce, though he did not rule out an extension of the law if further measures are needed.
He said the general advice to drivers remained that they should turn their phones off while driving, and pull over if they needed to make or receive a call.
A survey of 1,000 motorists by Tesco suggested more than nine out of 10 drivers were unaware of the changes.
A separate study by Sainsbury's said that almost nine million people used a hand-held mobile phone while driving during the last year.
Of those 709,000 said that using their phone has nearly caused them to have an accident.
A spokesman for the bank said: "Our research reveals that 10% of motorists key in text messages while driving, 15% read messages and 16% answer calls."
But a roadside straw poll by Roger Harrabin, correspondent for BBC Radio 4's Today programme, suggested mobile phone use by drivers had slightly declined compared to last year.
In his rather unscientific study - conducted by standing at a busy junction in north London for an hour - he spotted only two drivers using hand-held mobile phones compared to eight in an hour last year.
However, he did see rather a lot of drivers evidently using hands-free kits and holding earnest conversations with their dashboards - without paying full attention to the road.
Roger Harrabin says the new ban should be communicated forcefully to commercial van drivers, for whom using mobile phones while driving may have become a business imperative.