The architect of the flawed Horizon IT system, who provided evidence used to convict sub-postmasters, has claimed immunity before agreeing to appear at the public inquiry.
Gareth Jenkins, who is believed to have been instrumental in developing the software as a senior computer engineer at Fujitsu, is being investigated by police for his role in the Post Office scandal.
His testimony in court cases that Fujitsu's IT system was working properly was central to convictions and repeatedly used by Post Office lawyers.
Tracked down by The Telegraph at his home in Berkshire, 69-year-old Jenkins, when asked if he regretted what happened, said: "I don't want to talk. I have nothing to say to you."
Cannot be used against him
Mr Jenkins has twice sought assurances that any testimony he gives in the investigation will not be used against him in any potential prosecution, and his testimony has also been postponed twice.
Paula Vennells, the former Post Office director who presided over the scandal, said on Tuesday she was handing back her CBE and that she was "truly sorry for the devastation" caused to sub-postmasters who were wrongly prosecuted and convicted. It also emerged that she was eligible for the role of Bishop of London in 2017.
Ms Vennells said in a statement: "I have maintained my silence until now as I felt it was inappropriate to comment publicly while the investigation is ongoing and before I have given my oral evidence.
"I am, however, aware of the calls from sub-postmasters and others for my CBE to be returned. I have listened and confirm that I am returning my CBE with immediate effect."
Adam Crozier, the CEO of Royal Mail between 2003 and 2010 when it owned the post office, also issued a statement saying he felt "deeply sorry for those whose lives were devastated by what happened" but denied any involvement.
Sir Ed Davey, the Liberal Democrat leader who was then Post Office Secretary, is now under pressure to hand back his knighthood.
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Prosecutions brought by the CPS
The Telegraph can also reveal that at least 27 prosecutions have been brought by the Crown Prosecution Service - as opposed to the Post Office - raising serious questions about whether Sir Keir Starmer, the Labor leader, oversaw a number of wrongful convictions. as Director of Public Prosecutions between 2008 and 2013.
Mr Jenkins should have testified twice at the public inquiry. But it was postponed each time, including until November 2023, when the Post Office released 3,045 documents the night before he was scheduled to testify. Sources have speculated that the release of the documents was timed to prevent Mr Jenkins from testifying.
The Metropolitan Police confirmed last week that it was investigating "matters relating to Fujitsu Horizon and the Post Office... possible offenses of perjury and perverting the course of justice".
The Met also announced it was investigating "potential fraud offences" arising from the unlawful prosecution of sub-postmasters. This includes the accusation that the Post Office increased its profits by recovering money from sub-postmasters who were wrongly dragged through the criminal or civil courts.
The Telegraph has learned that Mr Jenkins, chief architect of Horizon at Fujitsu, told investigators as early as 2012 that the IT system designed for the post office was remotely accessed by Fujitsu at its headquarters in Bracknell, Berks. But it wouldn't be until 2019 that the Post Office would admit that subpostmasters' computer systems had been accessed remotely, blowing a hole in the plaintiff's main argument that the system could not be tampered with and was secure.
Ian Henderson, director of Second Sight, a forensic accounting firm that first highlighted the unsafe convictions, told the BBC on Tuesday: "We were able to identify that there were bugs and defects in the Horizon system. This was announced to the post office by Fujitsu itself.
"I visited Fujitsu in September 2012 and met the senior technical engineer and had a very detailed meeting discussing how they operated and what the issues were. During that meeting, Fujitsu disclosed to me that they were routinely using remote access to branch terminals to troubleshoot problems."
The Telegraph has learned that the senior engineer who briefed the Second Sight team was Mr Jenkins. It was not until 2015 that the prosecutions were stopped.
Documents forced a postponement
Mr Jenkins was due to give evidence to the inquiry for the first time on July 6, 2023, but on the eve of his testimony the Post Office produced 5,000 documents that it said had just come to light. The appearance was rescheduled for November 2023, but again more than 3,000 documents were found by the post office, this time days in advance, forcing the postponement.
Mr Jenkins has twice asked Sir Wyn Williams, the chairman of the inquiry, to ask the Attorney General to grant him immunity from any comments he makes during evidence to the inquiry so that they are not used against him in any future criminal proceedings can be used in court.
Both times Sir Wyn rejected his request. In October 2023, Sir Wyn said he would not seek a commitment from the Attorney General that would "restrict the use in criminal proceedings of evidence provided to the investigation as requested by former Fujitsu engineer Gareth Jenkins" .
He added: "I am satisfied that Mr Jenkins has not been the victim of dishonesty to date and I am determined that he should not be the victim of dishonesty as the work of the investigation progresses."
Politicians have demanded that Mr. Jenkins testify.
Kevan Jones, the Labor MP and member of the Horizon Compensation Advisory Board, said; 'Gareth Jenkins should appear before the public inquiry. The investigation considers him a key witness and therefore he must testify. If he doesn't appear, he must appear. What has been astonishing this week is the deafening silence from Fujitsu as a company. They need to come forward and explain what their role has been in all of this."
David Davis, the former Tory Cabinet minister who has pushed for justice for the sub-postmasters, said: "He should appear and testify. I can't think in what world he thinks he should get immunity since we need to investigate what happened.
"We cannot grant immunity just because people are going to give evidence at the public inquiry. Providing evidence is a requirement for their involvement in this case."