Horrified by Horizon? Then get ready to be totally appalled by AI

It doesn’t take much imagination to describe what happens when a large corporation, over 16 long years, is allowed vindictively to prosecute 900 subpostmasters for theft, false accounting and fraud, when shortfalls at their branches were in fact due to bugs in the accounting software imposed on them by that corporation, as “one of the greatest miscarriages of justice in our nation’s history”.

But then Rishi Sunak is not the most imaginative of men. The US Marines, on the other hand, have an economical term that fits the Horizon fiasco like a glove: it was a “clusterfuck” – primly defined by the Cambridge Dictionary as “a very rude word for a complete failure or very serious problem in which many mistakes or problems happen at the same time”.

Horizon was the product of a flawed and sometimes clueless IT procurement system to which the British state has for decades been addicted. The system eventually procured – from an offshoot of ICL owned by the Japanese giant Fujitsu – was a sprawling, computer bug-filled monster.

The idea was to replace the paper-based accounting system in post offices. But the rollout, starting in 1999 – to 13,000 busy, non-technical subpostmasters – was hasty, and training was inadequate for the scale of the transformation in the workflows involved. Users rapidly discovered bugs and deficiencies in the system, but found that Post Office management manifested a semi-religious faith in the technology – which led to subpostmasters being prosecuted, having their lives ruined and in some cases killing themselves.

Horizon was an electronic point-of-sale system that replaced paper-based tills. It was also networked, theoretically enabling the Post Office to have an overall record of cashflow across the country. But from the beginning, as the Guardian’s Alex Hern has pointed out, it seems that the system was “simply not up to the tasks placed upon it”.

As early as 2001, a team led by one of the system’s developers had found “hundreds” of bugs. A full list has never been produced, but some examples surfaced in court proceedings. In one, the “Dalmellington Bug” (named after the Scottish town where a subpostmaster first fell prey to it), the screen would freeze as the operator was attempting to confirm receipt of cash. Each time the user pressed enter on the frozen screen, it would silently update the record – and the subpostmaster was then held responsible for the results. You can imagine the consequences.

The strangest part of the story is how long it took for the truth to dawn on the political system. Journalists had been doggedly telling the story of Horizon’s victims ever since Computer Weekly broke the story in 2009. Trade paper the Press Gazette reckons that the magazine has published about 350 storieson it since 2009, mostly by Karl Flinders. Seventy of these came before the end of 2018 and the rest followed after the Justice For Subpostmasters Alliance brought a group action trial against the Post Office that year and a public inquiry began in 2020.

Despite this admirable journalism (and sterling work by a handful of MPs), it somehow failed to become a hot political issue until ITV screened Mr Bates vs the Post Office. Then the dam broke. As the BBC’s political editor Chris Mason put it, “Here we are, seven days later, and the prime minister stands in front of a packed House of Commons, and says the government will put forward a new law… How extraordinary. The power of drama. The momentum it has generated, the public opinion it has shifted, the government it has galvanised.”

If there is one big lesson to take away from the shambles, it’s this: at the root of the problem was the blind faith of a corporation in technology that it had expensively purchased. The Post Office bet the ranch on a traditional software system whose deficiencies could have been found by any competent investigator, because it was human-legible.

But there is now unstoppable momentum for organisations to deploy a new kind of technology – artificial intelligence – which is completely opaque and inexplicable. So it will be much, much harder to remedy the injustices that will inevitably follow its deployment. After all, Horizon merely couldn’t do accounting. The erroneous flights of fancy that AIs can sometimes produce, on the other hand, have to be seen to be believed.

John Naughton chairs the advisory board of the Minderoo Centre for Technology and Democracy at Cambridge

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