A former executive of Fujitsu, the company that developed the Post Office’s Horizon IT system, has told a public inquiry he felt “aggrieved” that what he thought was a “good system” had been placed into such disrepute by the scandal, and said he believed that the “real issue” was the way criminal prosecutions of post office operators had been handled by the state-owned body.

Richard Christou, the former chief executive and executive chairman of Fujitsu Services Holdings, was testifying at the inquiry, which is examining why the Post Office prosecuted and ruined hundreds of people, alleging financial shortfalls in their post office branch accounts. Despite campaigns, it took years for the Post Office to admit that faults with Horizon were behind many of the shortfalls.

Christou, who was chief executive between 2000 and 2004, was asked why no Fujitsu whistleblowers had raised concerns to him about the ability of Fujitsu staff to remotely access the Horizon IT system and to change the branch accounts of post office operators.

Flora Page, a barrister representing a number of post office operators, asked him: “Why were there no Fujitsu whistleblowers? Why did no one come forward?”

Christou told the inquiry he took issue with the description of “tampering” with branch accounts. “First of all, I don’t like the word tamper – that is a pejorative term,” he told the hearing.

“Secondly, my understanding is – and I knew nothing about this particularly at the time – these alterations were made in conjunction with the Post Office in order to correct various issues, that’s what I saw coming out of the evidence … Why no whistleblowers? You’d have to ask potential whistleblowers in Fujitsu. No one came to me and blew any whistles.”

Christou added: “I’m not mitigating that there is a gross miscarriage of justice and if you think I don’t feel for the postmasters and subpostmasters, you are wrong, I do,” he said.

“I feel aggrieved that what I thought was a good system has been put into disrepute, but I’m not responsible for it. I have said before, the real issue is the way the prosecutions were handled and flows of information. Why there were no whistleblowers and what they would have told me … I don’t know, he said.

The first person to come forward as a whistleblower was former Fujitsu employee Richard Roll, who gave an interview to the BBC’s Panorama about Horizon in 2015.

Christou said in his witness statement that he had had no knowledge of the prosecution of post office operators and said he had always regarded the rollout of the Horizon IT system as one of Fujitsu’s “major successes” and the Post Office as a “satisfied customer”.

More than 700 post office operators were wrongly prosecuted by the Post Office and handed criminal convictions between 1999 and 2015 as the Horizon system made it appear that money was missing at their branches.

On Wednesday night it was reported that the Post Office had accidentally published the names and home addresses of 555 post office operators wrongfully convicted in the Horizon scandal.

The Daily Mail said the dossier, which supposedly showed the details of those involved in suing the Post Office in 2019, including their postcodes, was on the website in full on Wednesday but later taken down.

A Post Office spokesperson said: “The document in question has been removed from our website. We are investigating as an urgent priority how it came to be published.

“We are in the process of notifying the Information Commissioner’s Office of the incident, in line with our regulatory requirements.”

Christou’s ex-colleague Duncan Tait, a former chief executive of Fujitsu Services Ltd, told the inquiry that he had said to Paula Vennells, then chief executive of the Post Office, that the Horizon IT system was like “Fort Knox”. Tait agreed he had made the comment but told the hearing that this was not about remote access to the IT system but about part of Fujitsu’s offices in Berkshire.

“Contrary to what she says in her letter, my comment was not about remote access to transaction data, but about physical access to the … developers’ area in Bracknell and the cybersecurity of the system,” he said.

The inquiry continues.