The German SS officer was fighting to save himself from the gallows for a terrible war crime and might say anything to escape the noose. But Fritz Knöchlein was not lying in 1946 when he claimed that, in captivity in London, he had been tortured by British soldiers to force a confession out of him.

Tortured by British soldiers? In captivity? In London? The idea seems incredible.

Britain has a reputation as a nation that prides itself on its love of fair play and respect for the rule of law. We claim the moral high ground when it comes to human rights. We were among the first to sign the 1929 Geneva Convention on the humane treatment of prisoners of war.

Surely, you would think, the British avoid torture? But you would be wrong, as my research into what has gone on behind closed doors for decades shows....