An accounting system used by Post Office sub-postmasters before the controversial Horizon software was introduced is likely to have also been faulty, an investigation has found.

A report said “there was a reasonable likelihood” that the IT system, called Capture, could have created cash shortfalls in accounts.

Capture was used in branches from 1992 to 1999, prior to the Horizon software, which has been at the centre of the Post Office scandal.

Post Office minister Gareth Thomas said he was “horrified” to learn about the issues with the Capture system.

Thomas said he had met with some sub-postmasters who used the Capture system and thanked them for “coming forward to talk about the impact it had on their lives and livelihoods”.

Between 1999 and 2015, more than 900 sub-postmasters were wrongly prosecuted after faults with Horizon made it look like money was missing from branch accounts.

The Horizon IT system has been at the heart of what’s been called the UK’s most widespread miscarriage of justice.

But Monday’s report from financial and risk advisory company Kroll has revealed fresh concerns over its predecessor Capture.

“We consider that, based on available evidence, there was a reasonable likelihood that Capture could have created shortfalls for sub-postmasters,” the report said.

Investigators said despite “various control functions being in place” at the Post Office, there was an “acknowledgement both in internal and external communications during the 1990s that Capture had bugs and errors that varied in severity”.

“In addition to this, the burden placed upon sub-postmasters to implement fixes, which varied in complexity, together with a reliance on communications from Post Office Limited to identify these bugs and fixes, meant there was a high capacity for errors to go unnoticed,” the report said.

Kroll did not comment on whether any convictions arising from sub-postmasters using Capture could be considered unsafe.

The government said it would examine the report and “consider what action should be taken” before making an announcement in December.

Kroll was asked in May to conduct an investigation into Capture to see if there was a reasonable likelihood the software could have incorrectly created shortfalls for sub-postmasters, following concerns that, like Horizon, there were known bugs and errors in the system.