Lee Castleton recalls to the last penny the shortfall that flashed on to his post office terminal on New Year’s eve, 2003 — ￡1,103.68. A week later another loss appeared, this time ￡4,230. Then another and another. By March, the sub-postmaster was ￡25,000 short. “I kind of knew from the second loss that this wasn’t a mistake on my part,” Castleton says.

With no means of interrogating the Post Office’s back-office systems, he called and emailed the IT helpline and his managers — 91 times. Yet all he received were instructions to do checks that he had performed dozens of times and, after some bland reassurances, the higher-ups stopped replying altogether.

An engineer technician, then briefly a stockbroker, Castleton had bought a post office in the seaside town of Bridlington, northern England, in the hope of providing a lifestyle that his young family would enjoy. Instead, a High Court judgment bankrupted him by ordering him to pay the Post Office the ￡321,000 it spent suing him for an illusory debt. Bankruptcy put paid to going back to stockbroking. So he had to make do as a jobbing engineer, sometimes sleeping in his car, in a hand-to-mouth struggle to meet the mortgage payments on the family’s flat above their now-defunct post office.