Nearly 4,000 drivers have been caught since the ban was introduced a year ago, raising £114,000 from the £30 spot fine.

Officers claimed there had been a “big reduction” in drivers using mobiles since the ban was enforced, after research revealed that response times in the car were up to a third slower while on the phone.

From today, drivers of lorries and coaches caught using hand-held mobiles will no longer be given the option of a fixed penalty but instead the offence will be dealt with at court. At court, car drivers face a fine of up to £1,000 and lorry and bus/coach drivers face a fine up to £2,500.

Malcolm Collis, Manager of Specialist Units within Thames Valley Roads Policing Department, said: “We have been enforcing this law for a year now and are noticing a big reduction in the numbers of motorists using hand-held mobile phones while driving.

”However there are still some motorists who are either ignorant of the laws or who flout them. These people need to understand the dangers of using a phone while driving. There are also dangers associated with hands-free phones. The only safe way is not to take calls while on the move.

“You are four times more likely to crash if you are using a mobile phone while driving. In our experience it is a frequent factor in road collisions in Thames Valley.”