A former senior Fujitsu engineer claims he was “trapped” into giving misleading evidence by the Post Office during the prosecution of subpostmasters accused of theft and fraud.

He told the latest Post Office scandal public inquiry hearing that what happened in cases where subpostmasters were wrongly convicted, based on the evidence he gave as an expert witness for the Post Office, was because of “how the Post Office behaved”.

On the final day of his evidence, Gareth Jenkins, once distinguished engineer at Fujitsu, said his role in court cases was “to tell the truth and answer the questions he was asked”.

But during his questioning over the three previous days inquiry, KC Jason Beer asked whether this was the whole truth, due to his focus on narrow questions about branches, ignoring the wider system.

In the latest hearing, Flora Page, barrister representing victims of the scandal, including Seema Misra, former subpostmistress who was wrongly convicted partly based on evidence Jenkins gave, accused Jenkins of being a “Fujitsu company man doing what the company wanted you to do. Protect the ‘monster’ [Horizon] created for the Post Office by Fujitsu.”

Jenkins said he did not believe Horizon to be a monster. Page put it to him that his role in the Misra case was to give Horizon a “clean bill of health”.

He said: “My role was to tell the truth.” Page asked if Jenkins tailored his evidence accordingly. He disagreed and said: “I attempted to answer the questions I was asked.”

Jenkins said he was sorry for what happened to Misra, but added that he felt that was down to the way the Post Office behaved. “I clearly got trapped into doing things I should not have done,” Jenkins told the inquiry.

Misra, who was pregnant at the time, was found guilty and sentenced to 15 months in prison. Following Misra being found guilty by a jury, Jarnail Singh, former head of criminal law at the Post Office, said: “Through the hard work of everyone, counsel Warwick Tatford, investigation officer Jon Longman and through the considerable expertise of Gareth Jenkins of Fujitsu, we were able to destroy to the criminal standard of proof (beyond reasonable doubt) every single suggestion made by the defence.”

Misra, who sat opposite Jenkins in the inquiry hearing, had her wrongful conviction overturned in 2021 at the Court of Appeal after a long campaign by subpostmasters to prove that the Horizon system, and evidence from it used in court, was unreliable.

Earlier this week, Jenkins agreed that he had developed a “sideline” supporting Post Office prosecutions. He was used as an expert witness in 15 prosecutions of subpostmasters from the early 2000s until he was dropped on the advice of an external barrister for giving misleading evidence.

He said the Post Office’s prosecutions appeared to be chaotic and he felt under pressure to give evidence to support it.

Jenkins recently resigned as a member of BCS, The Chartered Institute for IT, after he was informed the professional association could investigate his part in the widest miscarriage of justice in history.

During a recent public inquiry hearing, Ian Henderson, director at forensic accountancy firm Second Sight, which revealed problems with the Horizon system, described Jenkins as helpful during his investigation.

In an email to his business partner, Ron Warmington, during Second Sight’s investigation of Horizon from 2012 to 2015, Henderson said: “Gareth Jenkins has always struck me as, you know, straight as a die.”

Beer KC asked Henderson: “What was it in your dealings with Mr Jenkins that struck you and allowed you to say that he was straight?”

“He was not being evasive. [Jenkins] was happy to help, he was answering my questions, he provided promptly with follow-up material that I requested. I mean, there was no hesitation in his willingness to answer our questions and to provide assistance,” replied Henderson.

The Post Office scandal was first exposed by Computer Weekly in 2009, revealing the stories of seven subpostmasters – including Alan Bates – and the problems they suffered due to accounting software. It’s one of the biggest miscarriages of justice in British history (see below for timeline of Computer Weekly articles about the scandal, since 2009).

• Also read: What you need to know about the Horizon scandal •

• Also watch: ITV’s documentary – Mr Bates vs The Post Office: The real story •