Tougher penalties are not an effective deterrent against handheld mobile use by drivers as many are "returning to their old ways".

The RAC said a number of drivers changed their behaviour in the months after the punishment for illegal mobile use was doubled in 2017, but latest figures show the habit is "rocketing among some groups".

Nearly half of drivers aged 25-34 admit making or receiving calls with a handheld phone while behind the wheel, a survey indicated.

This is up seven percentage points year-on-year.

Some 29 per cent of motorists aged 35-44 say they use a phone to send texts, post on social media or check emails while driving, up 10 percentage points on the previous year.

More than 1,800 drivers were surveyed for the annual RAC Report on Motoring.

Since March 2017, motorists caught using a handheld phone have faced incurring six points on their licence and a £200 fine - up from the previous penalty of three points and £100.

RAC road safety spokesman Pete Williams said: "While the introduction of tougher penalties for handheld phone use at the wheel was absolutely the right thing to do, we fear any benefits have run their course with this data showing illegal use is now rocketing among some groups of drivers.

"Following the introduction of stronger penalties in 2017, we saw a promising shift with some drivers changing their behaviour for the better and becoming compliant with the law.

"Sadly, that didn't signal the start of a longer-term trend with drivers now seemingly returning to their old ways and putting themselves and millions of other road users at risk."

"There is still a huge job to do in communicating to drivers the dangers of continuing to mix driving with illegally using a mobile phone."

Forty-three people were killed and 135 were seriously injured in crashes on Britain's roads in 2017 in which a driver using a mobile was a contributory factor, Department for Transport figures show.