The Post Office is contacting 540 more people who may have been wrongfully prosecuted following the subpostmaster miscarriage of justice scandal.
The postal giant admitted hundreds more people may be affected – after 45 former employees were cleared of fraud due to a faulty computer system more than a decade ago.
Dozens of subpostmasters at the time were prosecuted for theft and false accounting because of the Post Office's defective Horizon accounting system which had "bugs, defects and errors" from the outset.
Last month, 39 former subpostmasters who were convicted and even jailed based on Horizon data had their convictions overturned by the Court of Appeal in a landmark ruling.
Seema Misra was pregnant with her second child when she was wrongly convicted in 2010. She was imprisoned despite insisting she was innocent.
The Post Office said it is contacting around 540 people with potentially relevant convictions and additional information is being sought in another 100 cases.
A spokesman said: "The Post Office sincerely apologises for serious historical failures. We continue to take determined action for people affected.
"Post Office has made strenuous efforts to identify individuals who were historically convicted and an extensive post-conviction disclosure exercise is taking place to identify and disclose all material which might affect the safety of those convictions."
Thirty-nine former employees walked free last month, after judges at the Royal Courts of Justice ruled that the innocent workers had been wrongly charged.
Lord Justice Holroyde said the Post Office "knew there were serious issues about the reliability of Horizon" and had a "clear duty to investigate" the system's defects.
But he added the Post Office "consistently asserted that Horizon was robust and reliable", and "effectively steamrolled over any subpostmaster who sought to challenge its accuracy.
The decision to free them puts an end to years of hardship for the former employees who say their lives have been "irreparably ruined" by the scandal which left them prosecuted for fraud.
Many of the workers told the court they had their livelihoods, homes and marriages destroyed after they were prosecuted by the Post Office - which knew the Fujitsu-developed IT system had "faults and bugs from the earliest days of its operation.
"Post Office Limited's failures of investigation and disclosure were so egregious as to make the prosecution of any of the 'Horizon cases' an affront to the conscience of the court," judges said.
Some of the other subpostmasters have since died, "having gone to their graves" with convictions against their name, while "some took their own lives", the Court of Appeal was told.
Lawyers representing the 42 former subpostmasters had argued serious defects in the Horizon system were "concealed from the courts, prosecutors and defence", in order to protect the Post Office "at all costs".
At the hearing in March, Sam Stein QC - representing five of the former subpostmasters - said the Post Office's failure to investigate and disclose serious problems with Horizon was "the longest and most extensive affront to the justice system in living memory".
He said the Post Office "has turned itself into the nation's most untrustworthy brand" by attempting to "protect" Horizon from concerns about its reliability.
He also argued that the Post Office's "lack of disclosure within criminal cases perverted the legal process", with many defendants pleading guilty "without exculpatory facts being known or explored".
Mr Stein told the court: "The fall from grace by the Post Office cannot be ignored.
"It has gone from valued friend to devalued villain.
"Those responsible within the Post Office had the duty to maintain not only the high standards of those responsible for any prosecution, but also to maintain the high faith and trust we had for the Post Office.
"Instead, the Post Office failed in its simplest of duties - to act honestly and reliably."
Tim Moloney QC, who represented the majority of the former subpostmasters, said the Post Office's failure to investigate the reliability of Horizon was "shameful and culpable".
He added: "Those failures are rendered all the more egregious ... by the inability of the defendants to make their own investigations of the reasons for the apparent discrepancies."
Mr Moloney told the court there was "an institutional imperative of acquitting Horizon and convicted subpostmasters ... in order to protect Horizon and to protect their own commercial reputation".
