Just one in 50 victims of America's deadly drone strikes in Pakistan are terrorists – while the rest are innocent civilians, a new report claimed today.

The authoritative joint study, by Stanford and New York Universities, concludes that men, women and children are being terrorised by the operations '24 hours-a-day'.

And the authors lay much of the blame on the use of the 'double-tap' strike where a drone fires one missile – and then a second as rescuers try to drag victims from the rubble. One aid agency said they had a six-hour delay before going to the scene.

The tactic has cast such a shadow of fear over strike zones that people often wait for hours before daring to visit the scene of an attack.

Investigators also discovered that communities living in fear of the drones were suffering severe stress and related illnesses.