One instructor, who runs a driving school in Essex, told The Telegraph that she would continue to use her top box on the motorway.“I don’t think I’d like to take learner drivers on the motorway with just ‘L’s on the back.” When you’re driving on a motorway and you’re a distance from a car or lorry, how are they going to see the ‘L’? It’s not as visible as the rooftop.” Driving instructors could be putting motorists at risk by taking learners on motorways, a report has warned, amid concerns that the top boxes on cars could fall off at high speeds. The guidelines, released by the NASP, an industry body representing more than 20,000 approved driving instructors, warned that the top boxes used to display the learner ‘L’ symbols may not withstand wind resistance at speeds of 70mph.A change in the law will mean that learners can drive on motorways from today, as long as they are with their instructor in a dual-controlled car. But the NASP has recommended that “consideration is given to the type of ‘L’ plates that are to be used” on instructor cars, and suggested that magnetic plates be used instead.“Many top boxes can be used at high speed, but it is advisable to check with the manufacturer about the maximum rated speed,” it said. A combination of “high winds” and age can mean that signs fall off of cars on the motorway, posing a hazard to other drivers. Mark Winn, the Driving and Vehicle Standards Authority (DVSA) Chief Examiner, told The Telegraph that a consultation with instructors (ADIs) had not raised significant concerns.“The majority of responders to the consultation did not think that there was an increased risk of using a top box and did not agree that they should be removed,” he said. The DVSA said that giving learners more experience on motorways could prevent them from staying on rural roads once they have passed their test, where accidents are more likely.Jesse Norman, Road Safety Minister, said: “Britain’s roads are among the safest in the world, but road collisions remain the second biggest killer of young people. “Allowing learner drivers to have motorway lessons with a qualified road safety expert will help more young drivers to gain the skills and experience they need to drive safely on motorways.” “Many organisations and driving schools also thought it was important to keep the top boxes so that people could easily identify learner drivers. DVSA are therefore leaving the use of top boxes to the ADI’s discretion and in accordance with manufacturers’ instructions.” Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.