Thousands of post office operators have complained they continue to suffer problems with the system at the heart of the Horizon IT scandal, with nearly all involving a financial shortfall.

As the final phase of the inquiry into the faulty computer system began, the results of a damning survey shows operators are still struggling with bugs in the system, that trust in the organisation is low and that they believe compensation should be higher.

Almost 98% of post office operators who participated in a survey as part of the inquiry into the IT scandal who continue to encounter “discrepancies” with the system have said the issue involved a financial shortfall.

Nearly 70% of the respondents to two anonymous surveys, which were sent to 16,000 post office operators before the start of the final phase of the live inquiry, which starts on Monday, said they had experienced an “unexplained discrepancy” on the Fujitsu-built IT system since January 2020.

The survey also found that post office operators from a minority ethnic background were more likely to have been threatened with suspension than those from a white background.

The report shows that eight post office operators said they had been suspended, or threatened with suspension, in the past three years after problems with discrepancies with the IT system.

In total, 80 of more than 1,000 respondents said that they had been threatened with suspension by the Post Office in the past. Operators from minority ethnic backgrounds were three times more likely to have been suspended and reinstated, YouGov found.

Gavin Ellison, the head of public sector and not-for-profit at YouGov, told the hearing that the findings were statistically significant.

Last year, documents released to campaigners revealed that lawyers investigating post office operators over the Horizon bugs used a racist term to categorise Black workers.

The document, which was published between 2008 and 2011, included the term “negroid types”, along with “Chinese/Japanese types” and “dark skinned European types”.

The public inquiry is examining the scandal, in which the state-owned body hounded post office operators for more than a decade, alleging financial shortfalls in their branch accounts and criminally prosecuting hundreds of people.

It has since emerged that these financial discrepancies were caused by IT bugs within Horizon. While 98% said they had encountered shortfalls, 34% also said the IT system produced surpluses in their accounts.

When asked how these discrepancies were typically resolved, almost three-quarters of respondents said they had to use either their branch’s money or their own to resolve the mis-balance.

The most common form of glitch in the system, for which Fujitsu has a £2.5bn lifetime contract, took the form of screen freezes or loss of connection.

Most operators said they felt “undervalued” by the Post Office and that it was not trying to improve its relationship with operators.

More than 68% disagreed that the Post Office was professionally managed, 65% said it was not a trustworthy organisation, and 55% disagreed with the statement that it had learned lessons from the scandal.

The second survey looked at the performance of the Post Office in relation to the various compensation schemes set up after more than 900 operators were found to have been wrongly prosecuted because of bugs in the Horizon system.

Just under half said they were dissatisfied with the Horizon Shortfall Scheme, while 47% of respondents said it was hard to understand.

“There was a sense that the process was too long, with a lack of transparency – for example, the cause of certain delays or information about how cases were progressing,” the YouGov survey said. “Some applicants surveyed believed that the amount of compensation received or offered was not sufficient, in particular to compensate for additional stress caused.”

Last week, it emerged that Nick Read, the embattled chief executive of the Post Office who is due to give evidence to the inquiry next month, is to step down next year.

The final phase of the inquiry, which is being chaired by the former high court judge Sir Wyn Williams, is looking into the practices and culture of the Post Office, as well as its delivery of compensation to wrongfully prosecuted post office operators.

As part of a move to repair relations and improve oversight, the Post Office appointed two operators as non-executive directors for the first time in 2021.

The directors, Saf Ismail and Elliot Jacobs, will give testimony this week. The final phase of the inquiry, in which more than 30 witnesses will testify, is due to finish in mid-November.

The Post Office has been approached for comment.