Incredibly, the victims of these snatch and grab operations were of no military, scientific or political value. Instead, they included a beautician, a schoolgirl and couples on romantic seaside dates who were suddenly whisked off to the most secretive country on earth.

For years, sensational stories of courting couples being carried off from beaches in the night by North Korean frogmen have filled the Japanese media. At first, few gave much credence to the tales, which seemed to be among the most unlikely of cold war fantasies.

But the rumours persisted and reports of failed ...