Vennells, who earlier this year gave back her Commander of the Order of the British Empire title that she received in 2019, admitted that she had “made mistakes” but denied there was a conspiracy to cover up the scandal.

“I have no sense that there was any conspiracy at all,” she said. “My deep sorrow in this is that I think that individuals, myself included, made mistakes, they didn't see things and hear things.”

After the Post Office introduced the Horizon information technology system 25 years ago to automate sales accounting, local managers began finding unexplained losses that bosses said they were responsible for covering.

The Post Office maintained that Horizon, which was made by the Japanese company Fujitsu, was reliable and accused branch managers of dishonesty.

Vennells, who was chief executive from 2012 to 2019, a period that included the last few years of the scandal, had for years insisted that the system was “robust” despite the hundreds of workers who said they had done nothing wrong.

Between 2000 and 2014, more than 900 postal employees were wrongly convicted of theft, fraud and false accounting, with some imprisoned and others forced into bankruptcy.

The number of victims is not fully known and the British government has introduced legislation to reverse the convictions.

"I did probe and I did ask questions, and I'm disappointed where information wasn't shared, and it has been a very important time for me to plug some of those gaps," she said in her first public remarks about her role in the scandal for nearly a decade.

The inquiry's chief counsel, Jason Beer, pondered whether Vennells was perhaps the “unluckiest CEO in the United Kingdom.”

Vennells, who insisted she was unaware of bugs in the Horizon system, is due to testify for three days." “One of my reflections of all of this – I was too trusting," she said.

When she was grilled about postmaster Martin Griffiths, who deliberately stepped in front of an oncoming bus in September 2013 and died weeks later, after he had been falsely accused of taking thousands of pounds from his branch, she broke down.

Vennells, 65, is also an ordained priest, apologised for her comment that subpostmasters had been “tempted to put their hands in the till” and said it was an “assumption” she made.

Questioned on whether she put the needs of the business over the suffering of subpostmasters, Vennells admitted there “will be many examples of where that is clearly the case."

A group of postal workers took legal action against the Post Office in 2016. Three years later, the High Court in London ruled that Horizon contained a number of “bugs, errors and defects” and that the Post Office “knew there were serious issues about the reliability” of the system.

The moment of reckoning was a long time in the making, but it was turbocharged by a four-part television docudrama that aired earlier this year.

The ITV show, “Mr. Bates vs the Post Office,” told the story of branch manager Alan Bates, played by Toby Jones, who has spent nearly two decades trying to expose the scandal and exonerate his peers. Vennells was portrayed by Lia Williams.

Despite hundreds of news stories over the years about court hearings and the continuing public inquiry, the show seen by millions rapidly galvanized support for victims of the injustice.

Vennells also said she didn't know for five years after she first joined the Post Office in 2007 that the company, which is state-owned but operates as a private business, had a unique function whereby it can prosecute its own staff, without the need to contact police or state prosecutors.