Duncan Tait, who was Fujitsu's chief executive between 2011 and 2014, made the comments to his Post Office counterpart Paula Vennells, who returned her CBE earlier this month.

Fort Knox is a highly secure US army building in the state of Kentucky. Its gold vault is surrounded by thick granite walls that are topped by a bombproof roof.

Hundreds of sub-postmasters and sub-postmistresses were prosecuted over claims they were stealing from the Post Office - but the missing money was actually due to Horizon software errors.

"As I have said before, I am appalled by the harsh treatment of the sub-postmasters and postmistresses," Mr Tait said in a statement to Sky News, as a public inquiry remains ongoing.

"As the public inquiry is already aware, I did refer to Fort Knox in a conversation with Paula Vennells."

Last Tuesday, the current chief executive of Europe for Fujitsu Services Paul Patterson admitted there was remote access to the Horizon system, despite repeated Post Office denials.

Nick Read, chief executive of the Post Office since 2019, denied he was aware, adding: "I've only been in the organisation since 2019, so it's difficult for me to comment."

Mr Tait said his comments were "in relation to the cyber and physical security of Horizon" and was "unrelated to the remote access issue".

"I fully support the inquiry and it would be inappropriate for me to comment further, ahead of giving my evidence," he said.

"This has been a terrible miscarriage of justice and like others at Fujitsu, I am sorry for the damage that has been done to the sub-postmasters and postmistresses' lives and any role that Fujitsu played in that."

The multinational is in the spotlight due to its role in miscarriages of justice - with recent ITV drama Mr Bates Vs The Post Office renewing public interest in the issue and sparking outrage.

Read more:
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Days after the show aired, Rishi Sunak announced those wrongly prosecuted in England and Wales could have their names cleared by the end of the year under fast-tracked legislation.

Those whose convictions are quashed are eligible for a £600,000 compensation payment, while Mr Sunak offered £75,000 to sub-postmasters involved in group legal action against the Post Office.

Lawyers have said that hundreds more victims could now come forward.

But campaigners, including former subpostmaster Alan Bates who was at the centre of the ITV drama Mr Bates Vs The Post Office, hit out at the "madness" of delays at processing compensation claims.