A former Fujitsu engineer has been accused by a lawyer acting for victims of the Post Office scandal of “hiding” problems with the Horizon IT system to protect the “out of control monster”, a public inquiry heard.

Gareth Jenkins, formerly a senior engineer at Fujitsu, which developed the Horizon IT system, faced tough questioning by lawyers acting for post office operators caught up in the scandal, which has been described as one of the biggest miscarriages of justice in recent history.

The Post Office prosecuted hundreds of operators, blaming them for financial losses in their branches when in fact the Post Office Horizon IT system was unreliable and had bugs, errors and defects. A public inquiry is examining what went wrong.

Jenkins was questioned about the criminal prosecution of Seema Misra, a post office operator who was pregnant with her second child in 2010 when she was convicted at Guildford crown court of theft and sentenced to 15 months in jail. She had to give birth wearing an electronic tag.

She was exonerated by the court of appeal in 2021. Jenkins was an expert witness for the Post Office at her trial.

Flora Page, the barrister representing Misra, likened the Horizon IT system to a “monster” and put to Jenkins that “hundreds of innocent people had already had their lives ruined to protect it but you don’t accept that do you?”

“I was not aware of that at the time, no.” Jenkins said.

“Isn’t the truth that you knew Horizon was a monster and that it was causing harm?” Page continued.

“No, that was not how I felt,” Jenkins replied.

“You hid it, didn’t you?” she continued.

“No, I did not,” he replied.

Page told Jenkins that Misra had been convicted on the strength of his witness evidence and he had not mentioned all “the body parts” of the flawed IT system including the hardware failures and “terrible code”.

Misra was at the inquiry watching as Jenkins was questioned about evidence he gave to her trial in Guildford, which had been seen by the Post Office as a test case of the Horizon system.

Page told Jenkins that he had “thrown mud in the jury’s eyes” and “hid all these problems when you gave evidence against Seema Misra, even though she was standing right there in the dock in front of you”,

Jenkins replied: “I don’t believe I deliberately hid anything.”

The inquiry continues.