Former managing director David Smith made the apology to the Post Office Horizon IT inquiry: "I would absolutely never think that it was 'brilliant news' for a pregnant woman to go to prison and I am hugely apologetic that my email can be read as such."

That victim, Seema Misra - who was sentenced to 15 months in jail and served four months while pregnant - said it wasn't good enough.

"They're apologising now, but they missed so many chances before," Ms Misra told Sky News.

"We had my conviction overturned, nobody came at that time to apologise. And now they just suddenly realised that when they have to appear in a public inquiry, they have to apologise."

The inquiry is investigating who knew what and when about the faulty accounting software that ruined lives, resulted in huge debts, ill-health, ruined reputations, and led to the conviction of hundreds of innocent sub-postmasters for theft and false accounting.

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The scandal received renewed attention after an ITV drama, Mr Bates vs the Post Office, aired early this year and brought to life how Horizon software, developed by Fujitsu, incorrectly generated financial shortfalls at Post Office branches throughout the UK.

"Brilliant news"

In 2010 Mr Smith emailed Post Office prosecutors, congratulating them on a job well done in jailing Ms Misra for theft.

"Brilliant news. Well done. Please pass on my thanks to the team," he said.

The message was intended to celebrate proving Horizon was robust, Mr Smith said, rather than someone going to prison.

"Regardless of the result, I would have thanked the team for their work on the case."

"However, seeing this email in the light of what I know now, I understand the anger and the upset that it will have caused and sincerely apologise for that," Mr Smith's evidence statement to the inquiry said.

"It is evident that my email would have caused Seema Misra and her family, substantial distress to read and I would like to apologise for that".

Ms Misra's conviction was overturned by the Court of Appeal in 2021.

A 'test case' that added confidence in Horizon

But it had been seen as a test case by Post Officials, Mr Smith told the inquiry.

The success of the case led to more confidence in Horizon, he added.

"I do know that from this point forward, we didn't really think about whether we should have an inquiry [into Horizon] again while I was at the Post Office and certainly if you looked at board minutes from the month after and the month after that which had been shared with me, we're not talking about Horizon at all."

"How can they do a test on a human being?", Ms Misra told Sky News, "I'm a living creature".

The legal representative for some sub-postmasters said the trial of Ms Misra was being "actively used by Post Office as part of [its] campaign to claim that Horizon was robust".

"Inherent risks" in Post Office prosecuting

The Post Office is allowed to investigate and bring prosecutions itself and does not require Crown Prosecution Service (CPS) involvement.

Reflecting on how prosecutions were carried out Mr Smith told the inquiry there are "risks" within the system.

In-house prosecution "can lead you to a position where you might not think as independently as you should do about the quality of the information", he said.

None of these issues occurred to Mr Smith during his tenure.

"I cannot recall thinking that any risk or compliance issues arose from [Post Office] undertaking this role, but with the benefit of hindsight, and in light of the wrongful prosecutions, I can see the inherent risks in the prosecutions taking place 'in house' and not by an independent enforcement authority."

At the time the organisation was too focused on other issues, such as Post Office separating from Royal Mail, the new coalition government, and the need to refinance the business, he said.

The company board was "pre-occupied" with investment from government, his witness statement said.

"Therefore, although we were aware of the case, at board level we were not heavily focused on it as our attention was on keeping the business running."