There were tears outside the High Court on Friday in a landmark judgement in favour of 550 former sub-postmasters who have spent years campaigning for redress.
The Justice for Subpostmasters Alliance claim the Post Office has abused its position to unlawfully suspend, sack, prosecute and criminalise people who run branch Post Offices.
Many were accused by the Post Office of stealing money.
The sub-postmasters claim discrepancies in their branch accounts were down to computer error.
The judge, making his first ruling in what could be a four trial litigation, found overwhelmingly in favour of the claimant sub-postmasters, castigating the Post Office witnesses for their "unsatisfactory" evidence which "did not stand scrutiny".
The Post Office had argued that due to the nature of the sub-postmaster contract it did not owe sub-postmasters a duty of good faith, fair dealing, transparency, and trust beyond the specific terms of their contract.
The judge disagreed and ruled that far from being a standard business contract, Post Office and sub-postmasters had a "relational" contract which puts responsibilities on the Post Office to recognise what the judge called their "uniquely unequal" relationship.
The evidence of Angela van den Bogerd, the Post Office's Business Improvement Director was singled out by the judge who said Mrs van den Bogerd "did not give me frank evidence, and sought to obfuscate matters, and mislead me".
The second trial in the group litigation (known as Bates and others v Post Office Ltd) is already underway, and next week Post Office witnesses will be cross-examined as to whether the Horizon IT system, which the Post Office insisted is "robust", is fit for purpose.
The Post Office on Friday said: "The judge's comments are a forceful reminder to us that we must always continue to do better.
" We have taken his criticisms on board and will take action throughout our organisation.
"Our postmasters are the backbone of our business, and our first priority will be to consider the points raised about the management of our contractual relationships and how we could improve them.
"There are, however, areas around the interpretation of our contracts where the judge's conclusions differ from what we expected from a legal standpoint and we are therefore seriously considering an appeal on certain legal interpretations."