Spy novels are littered with femme fatales who heartlessly deploy their womanly charms to coax state secrets from their lovers.

But according to the real-life inspiration for John Le Carre’s George Smiley, it is plain women, with good shorthand, who make the best secret agents.

Le Carre based his spy on John Bingham, 7th Baron Clanmorris, who had been the writer’s section head when he worked in MI5.