They are also watching movies on their phones from behind the wheel, said insurers MORE TH>N.
It said million of drivers are so addicted to their phones that they are suffering from a medical condition – Phone Separation Anxiety or Nomophobia.
The study was released as MORE TH>N launched its “Give Your Mobile The Boot” campaign to encourage drivers to leave their phones well out of reach in the boot.
The poll of 3,000 motorists found that nearly one in three admit to checking Facebook, Twitter and Instagram from behind the wheel.
Earlier this month the penalties for using hand held phones at the wheel doubled to six points on a licence and a £200 fine.
New drivers could be banned if caught on the phone just once as their threshhold is six points.
But the study found that on average every week 1,964,953 Snapchat, Instagram pictures and WhatsApp messages, 576,967 e-mails, 229,553 tweets and 508,975 Facebook posts are sent from the behind the wheel.
This is clearly a huge concern for safety on the road
Nine per cent of drivers – the equivalent of about three million motorists – admit to streaming an average of 2.5 hours a week each of video content from the driver’s seat.
That works out at a total of 1.9million hours’ worth of video being watched each week by drivers who should have their eyes on the road.
Studies have shown that drivers can have slower reaction times when they are texting than when they are over the drink-drive limit or under the influence of cannabis.
But the tougher penalties have had little impact with 41 per cent unaware of them.
Psychologist Amanda Hills said: “‘These results confirm there are growing numbers of people suffering from an addiction to their phones, which is clearly a huge concern for safety on the road whilst driving.”
And Kenny Leitch, global connected insurance director at MORE TH>N, said: “Our research shows that there continues to be a worrying amount of phone usage behind the wheel across the UK, in spite of the newly introduced harsher penalties for those caught doing so.
“Here at MORE TH>N we appreciate just how much a phone can be a distraction in the car, which is why our new Give Your Mobile The Boot campaign sets out to urge motorists to put their devices in the boot before their journey so they are not tempted to use it while driving.”