In Alan Turing’s world, at Bletchley Park, there wasn’t time to crack a PIN with brute force, as ciphers changed too often and lives were at risk.

The wooden huts hidden on a sprawling Victorian mansion’s grounds hummed like beehives – a munitions factory crossed with a mad inventor’s workshop. The mechanical groan of drums turning in lockstep, the constant whir of fans: this was Bletchley Park, where brilliant young minds in tweed wrestled with cracking state secrets between tea breaks and blackout drills.