The Post Office has been told by the Government to look into the case of a subpostmaster convicted of theft linked to a second IT system.

The firm is already at the centre of a scandal over the prosecution of subpostmasters using evidence from the flawed Horizon accounting software.

But the Government has now asked it to look into the case of Steve Marston, a 67-year-old former subpostmaster in Heap Bridge, Greater Manchester, who claims an earlier IT system – Capture – led to him being convicted of theft and false accounting offences in 1998.

The Department for Business and Trade has asked the Post Office to look into the case following reports in the i newspaper.

Officials expect the Post Office to take appropriate action if there are issues discovered with other systems currently or previously used by the firm.

A Post Office spokesman told the newspaper: “We take very seriously the concerns that are being raised about cases from before the Horizon system was first rolled out in 1999, and we will of course assist in looking into such cases brought to our attention.”

Mr Marston told the i he did not steal “a penny” but pleaded guilty to avoid being sent to prison.

“They said pleading guilty was the only way to avoid going to jail,” he said. “I just thought it must be something I’m doing wrong; computers were in their infancy, you didn’t think they could be wrong.”

Mr Marston says he told Post Office auditors that he was innocent, but was unable to explain what had happened.

“They said ‘Capture doesn’t make mistakes’,” he added.