The uncomfortable truth has been confirmed by a number of experts, from the head of the International Atomic Energy Agency to the US Defence Secretary. According to intelligence briefings shown to academic experts, North Korea has successfully miniaturised nuclear warheads that could be launched on medium-range missiles.

This puts it ahead of Iran in the race for nuclear attack capability, and significantly alters the balance of power between North Korea’s large but poorly equipped military and the South Korean and US forces ranged against it…

North Korea carried out an underground nuclear test in 2006, but until recently foreign governments believed that such nuclear devices were useless as weapons of war because they were too unwieldy to be mounted on a missile.