Up to five million European motorists with an undiagnosed illness are at increased risk from falling asleep at the wheels of their cars, according to research by the European Respiratory Society (ERS).

Sleep apnoea causes sufferers to stop breathing five times each hour while they are asleep at night and can result in drowsiness during the day as well as excessive fatigue and a lack of concentration.

The severe form of the condition affects up to 8 per cent of men between the ages of 40 and 60 and 2 per cent of women.

The ERS is suggesting that drivers with sleep apnoea should be legally required to declare their condition. In the UK, Spain, Netherlands and France, sufferers must follow treatment or face losing their licences.

The ERS's sleep aponoea task force chairman Patrick Levy, University Hospital Centre of Grenoble, said: “This situation is even more regrettable in view of the fact that there is now an effective treatment for the condition which involves a nasal mask worn nocturnally to provide continuous positive airway pressure.”