Director sets out to unmask the secret underwater agent known as Hvaldimir in new documentary

When a white whale, mysteriously kitted out with covert surveillance equipment, was first spotted in icy waters around Norway five years ago it seemed like an improbable chapter from a spy thriller. But working out the true identity and secret objectives of this beluga, nicknamed Hvaldimir by the Norwegians, quickly became a real-life puzzle that has continued to fascinate the public and trouble western intelligence analysts.

Now missing clues have surfaced that finally begin to make sense of the underwater enigma. The makers of a new BBC documentary, Secrets of the Spy Whale, believe they have traced the beluga’s probable path and identified its likely mission.