Public and political interest in the industrial-scale miscarriage of justice suffered by sub-postmasters was transformed by a television drama.

Since 2020 retired judge Sir Wyn Williams has been probing the circumstances that led the Post Office to prosecute more than 900 sub-postmasters for theft, fraud and false accounting caused not by dishonesty, but errors in the Horizon software it required them to use, since 2020.

This necessarily painstaking process has been conducted in public throughout, with dozens of evidence sessions aired live on YouTube, with transcription and hundreds of documents available in full online.

Follow the latest stage of the public inquiry live on Sky News and at news.sky.com from 10am today

Only since Christmas, and the airing of ITV's Mr Bates Vs The Post Office, which measured this long and complex scandal by the human cost to those wrongly convicted, has it gained traction in Westminster and the media.

The penultimate phase of the inquiry will begin, fittingly, with a full day of evidence from the eponymous hero of that drama Alan Bates, the indefatigable sub-postmaster who led a group litigation against the Post Office in 2017.

His evidence will set the context for appearances by senior executives of the Post Office and Fujitsu, which built the Horizon software, and politicians who took key decisions during more than a decade of malfunction and alleged manipulation of the system.

Former Post Office chief executive Paula Vennells will face questions for three days in May, and former Royal Mail Group chief executive Adam Crozier will appear at the end of this week.

Politicians including Liberal Democrat leader Sir Ed Davey and Labour campaign director Pat McFadden will also be in the chair to answer for their actions as Post Office ministers.

A key question for all of them will be what they knew of the problems with the Horizon system and when.

In 2019, the group litigation led the High Court to rule that the software contained "bugs, errors and defects" that could have caused the shortfalls on which the Post Office based its convictions.

The evidence that Post Office officials knew their system and therefore their prosecutions were flawed has mounted even since the ITV drama.

A 2017 report by Deloitte, published by the inquiry last month, found examples of branch balances being changed remotely to order, something the Post Office had long insisted could not be done.

Last week, Sky News revealed audio recordings of phone calls between independent investigators and Post Office executives in 2013, in which allegations of remote tempering of branch accounts by their Fujitsu counterparts were discussed.

Ms Vennells and her former colleagues will also have to answer for their role in directing the Post Office to continue prosecutions even after being alerted to these flaws, and to commit millions in legal costs to try and outspend sub-postmasters who fought back.

On Ms Vennell's watch, the Post Office settled the group litigation for £58m, of which £47m was swallowed in legal costs, leaving 555 sub-postmasters, some of whom were wrongly jailed, to share just £11m, less than £20,000 each.

Sir Wyn Williams has committed to producing recommendations as soon as possible after the inquiry concludes in September, but the drama has already prompted the government to address some of the biggest issues.

Legislation has been tabled that will at a stroke exonerate all prosecuted sub-postmasters who meet certain conditions, a move that has disturbed some in the judiciary and ministers admit carries the risk of clearing those guilty of crimes.

The aim is to make all sub-postmasters eligible for compensation, which requires convictions to have been overturned, but even that process is mired in controversy.

There are three separate schemes, all run by the Post Office.

A parliamentary select committee in February heard evidence from lawyers for the victims that they are slow, overly bureaucratic and could even now take up to two years to deliver financial redress.

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That same hearing also exposed chronic dysfunction among the current Post Office management, with chief executive Nick Read revealed to be under investigation for alleged bullying of a former HR director, and allegations of a smear campaign against the former chairman Henry Staunton.

There is more than enough material in this sorry, squalid corporate scandal for a made-for-TV sequel.

Alan Bates and his peers will settle for redress and real world recriminations, including potential criminal prosecutions, for those responsible.