Pilots should be made to undergo “tiredness tests” before they fly to help stop them from falling asleep in the cockpit, MPs have been told.

The British Airline Pilots' Association (BALPA), which represents over 10,000 UK pilots, warned politicians that lethargy affecting captains and first officers presented the single biggest threat to plane passenger safety.

The union said it wants airlines to use computer programmes to estimate pilots' fatigue levels based on their flight rosters, which are created weeks in advance of their duties.

Long working hours and regularly crossing different time zones are said to contribute towards severe tiredness inside plane cockpits.

Under rules set by the European Aviation Standards Agency, which regulates working hours, pilots who declare they are too tired to safely lead a journey are not compelled to fly.

However, it is claimed aviators are still operating flight controls over fears they could be penalised or even lose their jobs if they report being too fatigued to work.

BALPA has proposed airlines could use a computer based model based on the Karolinska Sleepiness Scale, a study used to measure an individual's drowsiness.