Former Post Office boss Paula Vennells “slavishly” maintained the position that the Horizon system was robust despite knowing it was faulty, her former Royal Mail Group counterpart has said.

Dame Moya Greene told the Horizon IT inquiry she initially sent messages of support to Ms Vennells because she believed the ordained priest had been “vilified” for her role in the scandal.

The inquiry heard that Dame Moya changed her stance after seeing evidence emerge from the inquiry which led her to believe the former Post Office chief executive knew about Horizon faults.

In an exchange of messages before she accused Ms Vennells of knowing about the system errors, Dame Moya told her: “What a terrible time. Just tell the truth.

“I know you are a good person and friends will be hard to find now.

“What has happened is a terrible… horrible thing. So many lives ruined. Yours too.

“Just tell the truth – what you knew, what you thought at the time, what they told you and mistakes you made.”

She later told Ms Vennells, in an exchange previously shown to the inquiry during the former Post Office boss’s evidence: “When it was clear the system was at fault, the PO should have raised a red flag, stopped all proceedings, given people back their money and then tried to compensate them for the ruin this caused in their lives.”

After Ms Vennells agreed the toll on everyone had been “dreadful”, Dame Moya added: “I don’t know what to say. I think you knew.”

On Friday, counsel to the inquiry Sam Stevens asked: “What did you think Paula Vennells knew?”

Dame Moya replied: “Gosh. I think she knew, on the basis of the evidence that has emerged in this inquiry, that there were faults in the system.

“I think that Post Office executives, including Mrs Vennells, continued to – slavishly, in my opinion – adhere to the position that was not tenable on the basis of the evidence presented here – that there were no faults.”

Dame Moya’s message from May 2022 read: “Horizon is the villain here and thank god we finally learned about the frailty in the system.

“We think of it is computerised, it is untamperable, infallible… not so.

“Stand tall. I know you are a good person and would never, never accuse anyone in the wrong.”

Asked what she meant when she said Ms Vennells was “a good person and would never accuse anyone in the wrong”, Dame Moya said: “Mrs Vennells was being vilified in the press and we didn’t know at that time in 2022 what we know now as a result of the evidence that has emerged in this inquiry.

“So at that time, I can only say what I saw – and what I saw when I worked with Mrs Vennells was a hard-working executive who was a problem solver. Not at all the kind of person that she has been portrayed (to be).”

Former Liberal Democrat leader Jo Swinson also gave evidence on Friday, saying Ms Vennells told her “with something of a pained expression” that subpostmasters “had their fingers in the till”.

The ex-postal affairs minister said Ms Vennells was trying to convey the message that “although these might seem to be lovely people, clearly some of them are actually just at it”.

She said she was reassured that Ms Vennells “spoke not only with the standing of a CEO of a major institution, but also with the moral authority of an ordained vicar”.

Ms Swinson, who was postal affairs minister between 2012 and 2015, told the inquiry she recalled “probing Paula Vennells on matters relating to Horizon on several occasions in person”.

She also said Ms Vennells “knew there was a problem with an unsafe witness, and she never told me”.

The ex-Lib Dem MP was referring to leading Fujitsu engineer Gareth Jenkins, who is the subject of a Metropolitan Police investigation on suspicion of perjury and perverting the course of justice.

Ms Swinson described a memo labelling Mr Jenkins as an unsafe witness as a “bombshell”.

She told the inquiry she “did not ask many questions” about the nature of the government’s role as shareholder of the Post Office and wished she had “intervened more”.

She added that she was “really sorry that I asked lots of questions and it wasn’t enough”.

More than 700 subpostmasters were prosecuted by the Post Office and handed criminal convictions between 1999 and 2015 as Fujitsu’s faulty Horizon system made it appear as though money was missing at their branches.

Hundreds of victims are awaiting compensation despite the previous government announcing that those who have had convictions quashed are eligible for £600,000 payouts.