Road safety charity IAM RoadSmart and Auto Express, the UK’s biggest-selling car magazine, teamed up to find out which are the deadliest behind-the-wheel distractions with programming a sat-nav found to be the worst.

Auto Express consumer editor Joe Finnerty was put to the test alongside British Formula 3 hopeful Jamie Chadwick in a professional racing simulator at Base Performance Simulators in Banbury. They were both assessed to see how they coped with the most common distracting tasks on UK roads, while completing timed laps and braking at a specific point. On hand was IAM RoadSmart’s head of technical policy, Tim Shallcross, to monitor the findings.

The results proved shocking, with a massive difference in performance between distractions. Entering a postcode into a sat-nav app proved to be the worst, followed by sending a text message. Other tasks carried out included eating, drinking, making a phone call and talking to a passenger.

Tim Shallcross said: “There was still a significant speed reduction for Joe when using a sat-nav, and even the ultra-focused Jamie completely missed the stop line. The moral? Those warning screens about not entering details on the move are there for a reason – don’t ignore them.”

On texting Tim said: “Joe would have been a menace to other road users; the car was more or less out of control. Jamie’s caution reduced the distraction in critical zones, but a sudden incident would have left her unable to take avoiding action.”

The least distracting task for lap time was talking to a passenger, but it still ranked very poorly for the braking test. Tim said: “It was the least distracting of all in terms of lap times, but interestingly, both drivers failed to brake accurately at the target line. Their ability to drive normally confirms the difference between the extra distraction of a phone conversation and the natural act of talking to a passenger, but still shows that any distraction reduces attention, and in an emergency, it might be critical.”

Steve Fowler, Auto Express editor-in-chief, said: “These results highlight just how important it is that drivers give their full attention to the road ahead. We’ve seen the staggering numbers of people who are still using phones at the wheel and these tests show how dangerous they can be – whether it’s texting, calling or programming the sat-nav. More work needs to be done to target those who still think it’s acceptable to use a phone while driving.”