Post Office admits computer system at centre of sub-postmaster prosecutions had bugs

However PO says probe into Horizon software justifies its 'confidence in the overall system'

The Post Office has admitted that a computer system at the centre of a legal dispute with several of its sub-postmasters suffered software bugs.

Some of the Post Office's 11,500 sub-postmasters have lost their homes and even been imprisoned as a result of legal disputes that followed the introduction of the Fujitsu-built Horizon accounting system.

Some 100 sub-postmasters claim accounting errors made by the software led to them being wrongly prosecuted for embezzling funds.

In 2012, the Post Office hired independent investigators Second Sight to begin examining the sub-postmasters' claims and, according to a BBC report, they found no "systemic problems with the core software", but did find "bugs" in the Horizon system.

Second Sight reported that an initial investigation by the Post Office failed to identify the fault in the system that caused the irregularities, as losses sometimes escalated.

One sub-post office in Hampshire was told it owed £36,000 due to unpaid losses of £9,000 escalating, leading to the sub-postmaster eventually lying to the Post Office and making out the books balanced. This led to a guilty plea of false accounting in court.

Another sub-postmaster spent his 60th birthday in prison as a result of incorrectly-calculated financial losses by the Horizon system.

Post Office chief executive Paula Vennells said that the "broad thrust" of Second Sight's review is "welcome".

Vennells said that the interim review shows that Horizon and its supporting processes "function effectively across the network".

Vennells added that Second Sight's report found that Horizon is used by 68,000 people across 11,500 UK branches to "successfully process... more than six million transactions every day" and that this finding "underlines... our cause for confidence in the overall system".

Questions over training and support for sub-postmasters, added Vennells, had also been raised by the review.