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The worker, who was convicted, attempted to overdose and eventually became homeless.

Teresa Williamson, one of the lawyers who prosecuted Lisa Brennan, said she now knows that management were aware of potential problems with the Horizon IT system but failed to tell those pursuing cases against sub-postmasters who were wrongfully convicted of stealing money.

“I trusted within the Post Office that if I asked for evidence it would be obtained,” she told the inquiry into the scandal, which is the biggest miscarriage of justice in UK history.

“I trusted that if there was unused material to be disclosed that would be provided to me by the investigator. Looking back, knowing what I know now… I realise there was a lot of material that wasn’t disclosed to me and things I should have known about that I didn’t know about.”

Ms Brennan worked as a counter clerk in a post office in Huyton, Merseyside. The Horizon system detected a shortfall of £3,000, resulting in her suspension. She appeared in court on Christmas Eve in 2002.

She was found guilty of 27 counts of theft and thereafter attempted to take an overdose. Her marriage broke down and she became bankrupt and homeless. Her conviction was only overturned in 2021.

“I assumed the data that formed the key basis for the decision to prosecute Ms Brennan was entirely accurate,” said Ms Williamson.

“I was not aware of any bugs, errors, defects or problems with the Horizon system at any point throughout my involvement in this prosecution,” she said.

“From my perspective as a lawyer, knowledge of these issues would have changed my approach to any prosecutions involving Horizon data.

“I feel gutted that I was unwittingly part of a horrible miscarriage of justice and am so sorry for the awful impact it has had on her life.”