By Adele Robinson, news correspondent
A damning report into the faulty Post Office IT system that preceded Horizon has been unearthed after nearly 30 years - and it could help overturn criminal convictions.
The document, known about by the Post Office in 1998, is described as "hugely significant" and a "fundamental piece of evidence" and was found in a garage by a retired computer expert.
Capture was a piece of accounting software, likely to have caused errors, used in more than 2,000 branches between 1992 and 1999.
It came before the infamous faulty Horizon software scandal, which saw hundreds of sub postmasters wrongfully convicted between 1999 and 2015.
The "lost long" Capture documents were discovered in a garage by a retired computer expert who came forward after a Sky News report into the case of Patricia Owen, a convicted sub postmistress who used the software.
Adrian Montagu was supposed to be a key witness for Pat's defence at her trial in 1998 but her family always believed he had never turned up, despite his computer "just sitting there" in court.
Mr Montagu, however, insists he did attend.
Liam Byrne, the Labour MP and chair of the business and trade committee, will be speaking to Sky News after 8am.