The
Eye started covering the Horizon debacle in 2011 after being approached by an obscure BBC local radio journalist named Nick Wallis. Wallis had been covering the case of Seema Misra (convicted and jailed while pregnant) and had done some methodical digging. He also poked the BBC to report the story, though not at national level. This led to the first whistleblower from Fujitsu/ICL coming forward.
It should be noted that this was not the first media coverage on the scandal. In 2009 Computer Weekly broke the story with detailed allegations of faults, meticulously researched and written by Rebecca Thomson and Tony Collins (the latter was the editor and persisted in the story despite denials and legal threats) and Sion Tecwyn covered it for BBC Wales (in Welsh).
From then on the
Eye and Wallis persisted with the story, culminating the the 2020 piece
Justice Lost In The Post, which led to an award winning BBC radio series. This led to a more detailed investigation which Wallis published in his book,
The Great Post Office Scandal in NOV2021.
There are lots of details on
Nick's blog. Drop him a few quid if you can, he deserves it.
Hope this helps.