The Post Office has conceded appeals by former sub-postmasters to overturn convictions linked to the Horizon accounting scandal.
The company said it is not opposing 44 of the appeals in which it acted as prosecutor.
Sub-postmasters were wrongly accused of theft, fraud and false accounting after the Horizon IT system was introduced to Post Office branches in 1999.
Post Office chairman Tim Parker said: “I am sincerely sorry on behalf of the Post Office for historical failings which seriously affected some postmasters.
“Post Office is resetting its relationship with postmasters with reforms that prevent such past events ever happening again.
“Post Office wishes to ensure that all postmasters entitled to claim civil compensation because of their convictions being overturned are recompensed as quickly as possible.
“Therefore, we are considering the best process for doing that.”
In addition to full co-operation with the Criminal Cases Review Commission’s review, the Post Office said it has set up an extensive disclosure exercise, by external criminal law specialists, to identify material which might affect the safety of any relevant historical prosecutions.
Solicitors acting for some of the sub-postmasters said it was a “landmark moment”.
It comes as the Commons Justice Committee called for more safeguards for private prosecutions to make sure they were fairer.
Hudgell Solicitors, which represented 33 clients, said their convictions, which have been against the names of many for a decade or longer, will now be quashed by the Court of Appeal.
Solicitor Neil Hudgel said: “For the Post Office to concede defeat and not oppose these cases is a landmark moment, not only for these individuals but, in time, potentially hundreds of others.
“We are obviously delighted for the people we represent. Clearing their names has been their driving goal from day one, as their reputations and livelihoods were so unfairly destroyed.
“We must never forget that these people endured years of suffering and how these allegations and convictions affected not only the individuals themselves, but their loved ones too.
“We have secured what amounts to a clear admission from the Post Office that people were convicted of crimes on the basis of unsafe and unreliable evidence.”
Four years after losing her husband Julian to bowel cancer, and 12 years after he was convicted of false accounting by the Post Office, 65-year-old Karen Wilson has spoken of her determination to clear his name.
She said Julian was “meticulous” in his running of the Post Office, which they bought in Astwood Bank, Worcestershire in 2001.
After a profitable first couple of years, he started experiencing troubles with the Horizon system.
When auditors finally arrived he was “delighted” as he believed the issues would finally be resolved.
At the time the accounts had a shortfall in excess of £27,000, and Julian handed over nine years’ worth of accounts for the auditors to look through.
He was suspended and told his only option was to plead guilty to false accounting, as that would prevent him from going to prison.
The couple had to sell their Post Office to pay back the money which was alleged to have gone missing.
“He was given 300 hours community service and he used to have to go out cleaning graveyards with other criminals.
“It was heart-breaking seeing my husband, who had done nothing wrong, having to do that,” said Karen.
“He knew it was the system right from the start but nobody would listen. Nobody wanted to listen. I have been determined to see this through to clear his name and have his conviction overturned.”
Karen added that constant issues and an increasing unexplained shortfall played more and more on her husband’s mind, so much so that one Saturday morning he left all the shutters down on the Post Office and told her “I can’t do this anymore”.
He was suspended, and his house was searched by the fraud squad, said Karen, adding: “They were asking things like ‘where’s the money, where’s the car and where have you been on holiday’, but again Julian handed over all of our personal accounts and business accounts as he knew there was nothing to find.
“He was still of the mind that all would be sorted and that we’d go back to running the Post Office, but then we got a call telling us to get a solicitor as he was going to be questioned under caution.
“When he came back from that interview he told me they’d been trying to bully him into saying he’d taken the money, saying things to him like it would be easier if he just admitted it.
“They dropped the charge of theft because there was no evidence of Julian having taken any money, because he hadn’t, but he was frightened into thinking that if he continued to deny everything he’d be found guilty and jailed. He said to me he simply couldn’t risk going to prison.”