At the height of the Second World War, a crack MI5 unit was given the task of taking down the enemy in the skies over Britain.

Not the Luftwaffe – but the peregrine falcon.

The hawks were picking off homing pigeons returning from Europe with vital information. Some pigeon owners even feared they were German-trained and working for the Nazis. So the Falcon Destruction Unit was born.

The five-strong armed team covered the south coast, led by a retired Irish colonel and champion shot. They would scour the clifftops for nests, and abseil to set spring traps. Birds not caught in traps were shot.

Details of the unit are contained in a book, Secret Pigeon Service by Gordon Corera, the BBC’s security correspondent.