I’ve just finished writing a book that took me into the world of Russian-British double agents during the cold war. I watched these people hop between countries, haunt British prime ministers and (if they were Russians) get killed. (British traitors, especially posh ones, usually walked away scot-free.)

Little has changed today. Russian double agent Sergei Skripal and his daughter Yulia are lying critically ill in Salisbury, weeks after being attacked with a Soviet-era nerve agent. The former Soviet secret policeman Vladimir Putin is recreating the world that shaped him: cold-war spying. Putin can manipulate us because he has learnt that in espionage, it’s not generally the secrets that matter. It’s the reaction of the public, media and politicians whenever spies are exposed to the light.

For two countries that didn’t have much to do with each other until rich Russians colonised central London this century, Russia and the UK have long engaged in vast mutual spying. But most of it was useless. British double agents such as Kim Philby and Guy Burgess often complained that the Soviets ignored their finds. Many of the British documents that Burgess gave the KGB weren’t even translated into Russian.