The favourite pastime of motorists – chatting on hands-free mobile phones – is as dangerous as drink-driving. Research has found using a mobile phone on Bluetooth with a headset while driving results in a drop in concentration equivalent to being over the drink limit.

Hands-free calls are currently legal but motorists engaged in conversation take a fifth longer to apply brakes and are less aware of other traffic. It has been illegal to hold a phone while driving for years and penalty points and heavy fines are applied to offenders. But the latest research using simulators for motorway driving show that over 97 per cent of us can only fully concentrate on one thing at a time. The remainder are regarded as super-taskers.

The volunteers who were monitored took 20 per cent longer to apply the brakes when they were on the phone. The average following distance also increased by 30 per cent which the researchers say this proves that drivers are failing to keep up with the pace of traffic around them.

The research carried out by professors at the University of Utah also showed that memory performance on words given to the volunteers decreased by 11 per cent and by three per cent on simple maths problems.