An investigator who helped to convict sub-postmasters labelled them as ‘all crooks’ when questions were asked about their convictions, the Post Office Inquiry has heard.

Internal emails among Post Office investigators showed that long-serving employee Gary Thomas was dismissive of sub-postmasters when their cases were made subject to assessment by the Criminal Cases Review Commission in 2015 - long after doubts had been expressed about the reliability of the Horizon IT system.

Thomas emailed his colleague to say he wanted to prove there was ‘FFFiiinnn no case for the justice of thieving subpostmasters’ [sic] and that ‘we were the best investigators they ever had and they were all crooks’.

Thomas, giving evidence to the inquiry, said his words then were ‘absolutely disgraceful’. He added: ‘My inference here, that everybody was guilty, is wrong and I’m embarrassed, is all I can say.’

Thomas was the lead investigator into Julian Wilson, who was sub-postmaster at Astwood Bank Post Office in the Midlands. Wilson was wrongly convicted of false accounting in 2008 and he was sentenced to 300 hours of community service, as well as being ordered to pay back thousands of pounds. He died in 2016 before his conviction was overturned.

Interviewed at his home address in 2008, Wilson immediately raised the fact that he had been having problems with Horizon. These problems had already been dismissed by Wilson’s line manager, but Thomas said in the interview his belief was that postmasters had been ‘up to no good’.

Thomas told the inquiry he now accepted he had been ‘completely wrong’ to say this and that his words to Wilson were inappropriate.

The inquiry heard that when he wrote up the offender report 11 weeks after interviewing Wilson he did not include any of the allegations made about the Horizon system. Indeed, he wrote in bold that ‘there did not appear to be any further failings in security, procedures or product integrity that directly affect this case’. When Thomas prepared his witness statement for a committal bundle, he again made no mention that Wilson had raised problems with Horizon. Thomas told the inquiry he now felt the investigation into Wilson’s case was ‘poor’.

Thomas said he was given ‘very minimal’ training during his 12 years on the security team, and prior to joining the team he had no experience of conducting criminal investigations or knowledge of criminal law.

Thomas has explained in his witness statement that he would always give disclosure to any legal representative who was present in interviews. But he admitted that if someone was unrepresented and acting in person he could not remember giving them similar disclosure.

He said it was not common for him as an investigator to challenge the Post Office lawyers in respect of the appropriate charges against a sub-postmaster. The exception was senior Post Office criminal lawyer Jarnail Singh, who Thomas said ‘didn’t come over quite as competent’ as others on the legal team. On one occasion, the inquiry heard, Singh had suggested five theft charges against an individual, only for Thomas to challenge this and suggest instead a charge under the Fraud Act.

Thomas accepted it was a ‘massive’ problem that investigators did not typically request the type of data that might have shown there was an error with the Horizon IT system causing shortages in branches. He received no training in how to interpret this data and said he was ‘pretty much self-taught’. Asked if this was adequate, he replied: ‘No, not at all.’