Motorists in England and Wales caught driving dangerously while using a handheld mobile phone face jail under new guidelines.
The new guidelines could extend to sending texts while driving
The Crown Prosecution Service guidance follows a policy change announced in September because of concerns that too many drivers flouted the ban.
Most drivers will still face the standard penalty of a fine and points.
But where driving falls far short of what is safe, prosecutors can press charges of dangerous driving.
When he announced the change in policy earlier this year, Director of Public Prosecutions Sir Ken Macdonald said such cases could include sending a text message while driving.
The Crown Prosecution Service says there are no plans to change the guidance on the prosecution of drivers caught using their mobile phones in Scotland.
Meanwhile, a major employer has banned the use of legal hands-free kits because of research suggesting they have no safety benefits.
One of the UK's biggest transport companies, FirstGroup, has announced that none of its employees will be allowed to use hands-free mobiles.
FirstGroup operates more than one in five local bus services across the UK, and trains including First Great Western.
The firm's bus and train drivers are already banned from using them and that will be extended to any staff on company business.
It follows findings by the Transport Research Laboratory that having a phone conversation could be more dangerous than drink-driving.
According to the research, a driver on the phone is more distracted than one who has drunk as much as the legal alcohol limit.
The risk of a crash was four times higher when the driver was on the phone, the study found.
Dr Nick Reed, from the laboratory, told the BBC that part of the danger from using a mobile phone was because the person at the other end could not see the driver.
He said: "Chatting to a passenger can be distracting, but what we found is that it's less so than having a mobile call.
"What we think that is to do with is that the passenger can see the traffic around you and can maybe pick up on your body language cues, and then modify the conversation accordingly."
The Parliamentary Advisory Council for Transport Safety, a charity which lobbies MPs, told BBC Radio 5 live that there was "still a hard core" of drivers who continued to use handheld mobile phones.
Executive director Rob Gifford said factors taken into consideration by prosecutors would include speed and overtaking.
"Those are all factors which the Crown Prosecution Service would consider and think 'yep, there was this incident, these things contributed to that incident taking place, therefore we'll lay a charge of dangerous driving rather than one of careless,'" he said.