A lawyer for the Post Office was warned by an investigator the case against a sub-postmistress was defective, the public inquiry into the scandal has heard.

Janet Skinner was jailed for nine months over an alleged shortfall at her Hull branch and she has previously told the inquiry her life was ruined by the wrongful conviction. She lost her house, could not get a job and was 'literally paralysed' for four months by stress.

Post Office investigator Diane Matthews, who interviewed Skinner, revealed to the inquiry on Friday that she told assisting lawyer Juliet McFarlane that she did not believe the sub-postmistress had stolen any money and there was no evidence to prove it. Matthews said she ‘didn’t really agree’ with the charges against Skinner but that ‘it was a case of "she’s the legally trained person who makes the decision".'

Asked by inquiry counsel Jason Beer KC whether McFarlane had pressed ahead with a theft charge despite the lack of evidence, Matthews said: ‘I can only presume that she thought there was some evidence in there that warranted that charge.’

Beer then asked: ‘Presumably, when she was sent to prison, leaving behind her two teenage children, you thought that was monstrously unfair?’

Matthews replied: ‘It’s never a good thing when people go to prison… it’s not something I take great pleasure in seeing.’

The inquiry heard that in another prosecution, that of Noel Thomas, casework manager Graham Ward had been ‘concerned’ about a draft statement from expert witness Gareth Jenkins which suggested that one reason for balance issues in branches could be ‘some sort of system failure’ and that such failures were ‘normal occurrences’.

Thomas, who worked for the Post Office for more than 40 years before he was also jailed for nine months for falsifying records, had insisted that the Horizon IT system caused apparent shortages in his North Wales branch.

Ward emailed colleagues to say the lines about system failure and normal occurrence were ‘potentially very damaging’ and he stressed the need to ‘ensure we are not embarrassed at court’. A new draft statement was prepared and sent to Jenkins, with Ward adding the original draft, with Ward adding: ‘This is a really poor choice of words which seems to accept that failures in the system are normal and therefore may well support the postmaster’s claim that the system is to blame for the losses!!!![sic].’

A further email from Ward urged that the expert’s statement ‘needs to included [sic] a paragraph which states that there is no evidence of a system error at Gaerwen (assuming this is the case)… We do not need to mention "system failures being normal occurrences" if there is no evidence of such a problem at this office.’

There was ultimately no mention that the shortages on the branch account may have been a Horizon system fault in the final signed witness statement.

The inquiry heard that Jenkins emailed Matthews before giving evidence in court for the Thomas prosecution, saying he had never been to court in any capacity and did not know what was required. Matthews replied it was ‘pretty much as you see on the TV really’.

In cross-examination, Beer asked: ‘Looking back, maybe with the benefit of some reflection, do you considered this to be adequate advice for a prosecution witness who had never give oral evidence in court?’

Matthews replied: ‘No.’

The inquiry heard that after Thomas was jailed, Matthews emailed colleagues and staff from Fujitsu – the suppliers of Horizon – to give details about his sentence. In the email, she said: ‘Mr Thomas was not expecting a custodial sentence and although not a particularly lengthy sentence, it does send out the right message.’

Asked by Beer what message she was hoping to send, Matthews said her email was a ‘cut and paste’ from a message from the Post Office PR team. She added that at the time the organisation seemed to be denying anything was wrong and had a strategy of ‘protect at all costs’.

The inquiry continues.