The clip shows the trucker holding both devices to his ears at the same time, completely letting go of the steering wheel to do so, before realising he’s been caught on camera.
The footage was captured on the M4 from the cab of another HGV being used by police to monitor driver behaviour as part of Operation Tramline.
The joint initiative between police forces and National Highways uses a number of unmarked HGV cabs to patrol some of the UK’s busiest motorways, giving officers an elevated view of vehicles to detect offences such as mobile phone use.
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Since its inception in 2015, more than 21,600 offences have been recorded by officers using the “supercabs”.
The most common two are not wearing a seatbelt - 6,253 instances - and using a handheld mobile phone (6,073).
Failing to wear a seatbelt carries a £100 fine, although there are plans to make it an endorsable offence. Using a phone is an automatic £200 fine and six penalty points.
Other common offences detected by the supercabs include drivers not in proper control of their vehicle (1,501 cases) and speeding (1,199).
Among the more bizarre cases reported are a driver caught eating a lasagne with a knife and fork while driving on a motorway and a trucker spotted boiling a kettle on the dashboard as he drove.
The footage has been released during a “fortnight of action” along the M4 and M5 that will see officers step up enforcement activity, carrying out vehicle safety checks and offering advice to drivers.
Nicholas Reed, National Highways’ road safety lead for the South West, said: “The HGV cabs are an important part of our commitment to tackling unsafe driving and those who take unnecessary risks with their own safety and that of others on the road.
“The number of people found using their mobile phone while driving is quite alarming. You are four times more likely to be in a crash if you use your phone and, if caught, face a £200 fine and six points on your licence.
“Through this fortnight of action on the M5 and M4 we want to make all of our roads safer by raising awareness and encouraging motorists to consider their driving behaviour.”