The 'five eyes' club was born out of Britain and America's tight-knit intelligence partnership in World War II and particularly the work at Bletchley Park, breaking both German and Japanese codes.

Code-breakers realised collaboration helped in overcoming some of the technical challenges and in being able to intercept communications around the world.

Out of this experience came what was first called BRUSA and then rechristened UKUSA - a top secret intelligence-sharing alliance signed in March 1946.