He added: “Indeed, I heard repeatedly that the subpostmasters’ claims regarding Horizon integrity were unfounded and that the system was working well.”
Also giving evidence on Wednesday, Mr Christou, who was chief executive of the company between 2000 and 2004, said he always regarded the Post Office as a “satisfied customer”.
He told the inquiry he “knew nothing about it” when he addressed his accountability for the miscarriages of justice.
Counsel to the inquiry Sam Stevens asked: “In terms of your accountability then, for the ICL Group and its operations, what would you say your level of accountability was?”
Mr Christou replied: “What I was responsible for was that, so far as possible, to see that the operations of ICL were carried out legally, were carried out profitably, and to report to my shareholders, Fujitsu Ltd, various issues in so far as it was necessary.
‘Miscarriage of justice’
“If you mean that I was responsible for the miscarriage of justice, then I don’t accept that.”
Mr Christou, who said in his witness statement that “no further problems” concerned with Horizon were raised with him during his time at Fujitsu, stressed during the hearing that he thought a “gross miscarriage of justice” had been committed.
Yet he added: “I really feel for the subpostmasters and the postmasters involved – but talking about accountability is a different matter.”
Ms Vennells, who gave evidence last month, broke down in tears on several occasions and apologised repeatedly for her part in the scandal.