The Post Office has been criticised for the way it handled IT problems that led to employees being accused of theft in a confidential report.
The document, witnessed by the BBC, says more than 150 sub-postmasters were wrongly prosecuted or made to repay money because of a technology fault.
Sub-postmasters are not directly employed by the Post Office, but are charged with running smaller branches.
The report says the IT system was not fit for purpose, despite the postal organisation claiming there was “no evidence” of systemic issues.
In 1995, a Horizon transactions processing programme was added to the Post Office and shortly afterwards, some sub-postmasters discovered money from bank machines, lottery terminals and tax disc sales did not match computer figures.
Because those employed in this position are held responsible for deficits at their branches, the deficiencies led to sub-postmasters being accused of theft or false accounting.
At the time, those who faced charges or fines claimed that investigators failed to look for the cause of root errors.
Investigators Second Sight compiled the report, which claims that IT training had not been good enough for those without any skills in the area.
It adds that outdated equipment had been installed and power cuts and communication problems only exacerbated the situation.
The majority of sub post offices remained unaffected by the technical problems, but the Post Office is now mediating with those who believe they have been treated unfairly.
The organisation still maintains that it is not aware of any technology problems.
“Although we will not comment on the contents of any confidential documents, after two years of investigation it remains the case that there is absolutely no evidence of any systemic issues with the computer system which is used by over 78,000 people across our 11,500 branches and which successfully processes over six million transactions every day,” it said in a statement.