I'm pretty sure this was the pilot for the original IT system that was supposed to allow benefit payments to be made through the Post Office. It was terrible and DWP (or whatever it was called then) withdrew and the project was foisted on the Post Office alone and rolled out in 1999. They knew right from the start, before the start, that it wasn't fit for purpose.
One of the earliest attempts to prosecute was withdrawn because they were forced to acknowledge that it wasn't fit for purpose:
Cleveleys Post Office boss lifted the lid on 'biggest miscarriage of justice in modern times'
It's unfortunate that the local paper has framed it like this. It's "despite Cleveleys proving the software was faulty way back in 2001, prosecutions continued until 2014 and the cover-up is still ongoing". But it's a reasonably short account of what happened back then.
Computer Weekly has done shedloads of reporting, their round up and links to dozens of articles since 2009 is here: Post Office Horizon scandal explained: Everything you need to know
(Most of their links are paywalled, but the internet archive has most of them, or will grab any new ones you offer it.)
Inquiry website and more searchable mirror.
E2A: managed to find the Computer Weekly summary too: Post Office tried to convince independent IT witness that he was wrong about Horizon
An email from Fujitsu’s Holmes to a colleague in June 2004 gave an account of a conversation he had with Mandy Talbot, a senior lawyer at the Post Office. This followed Wolstenholme rejecting a settlement with a trial date set.
“The Post Office are still taking advice as to how best to deal with this and [Mandy Talbot’s] view/belief was that the safest way to manage this is to throw money at it and to get a confidentiality agreement signed,” he wrote, adding that the Post Office was determined to keep evidence of Horizon problems secret. “[Mandy] is not happy with the ‘expert’s’ report as she considers it to be not well balanced and wants, if possible, to keep it out of the public domain. This is unlikely to happen if it goes to court.”