The former chair of a Whitehall agency responsible for taxpayers’ interest in the Post Office has blamed the Horizon IT scandal on a mixture of “incomplete curiosity” and “a toxic culture” at the state-owned company. Robert Swannell, a veteran City businessman and former Marks & Spencer chair, was speaking on Tuesday before the judge-led public inquiry investigating why post office operators were wrongly prosecuted for theft and false accounting over financial discrepancies linked to bugs within the Horizon IT system. Between 2014 and 2021 he led the agencies that help manage the government’s stake in state-owned businesses such as the Post Office and Channel 4, first being the chair of the Shareholder Executive until 2016, before taking the same post at its successor body, UK Government Investments (UKGI). Swannell told the Horizon inquiry that, in his view, what went wrong at the Post Office was partly down to a “closed, defensive culture” combined with incuriosity. “I’m afraid that when an incomplete curiosity … meets a toxic culture, bad things happen,” he said. Swannell added that in 2019, after a high court judge ruled against the Post Office in the first stage of a lawsuit brought by Sir Alan Bates and 554 other branch owner-operators, the UKGI board made the Post Office its top priority. “When I read the judgment … I noted that the language used by the judge was excoriating,” Swannell said in his witness statement. He told the inquiry that he had an “utterly visceral reaction” to the court ruling, given he “had heard for the previous years that there was nothing wrong with Horizon”. Swannell said: “It was clear to us then in 2019 that the culture at the Post Office was shocking, and by that I mean it was a closed, defensive culture that was not in the business of giving information. “I can’t tell you whether information was withheld deliberately or whether simply they didn’t give it. “But whatever the reason there were a whole range of things that should have been known to the board of the Post Office and then therefore to the UKGI board member [in the Post Office boardroom] and as a result of that to the UKGI board.” He added: “Had it happened you would have seen exactly what you saw in March 2019 … we would have been on it in spades.” In his witness statement to the inquiry, Swannell apologised for the pain and suffering of post office operators, which he said represented “a catastrophic failure by many people and organisations”. He said that since he “first appreciated how misguided POL’s [Post Office Ltd] stance had been, I have been determined to do everything I can to ensure that a tragedy like this can never happen again by learning the lessons from it and learning them well”. The inquiry continues.