Post Office inquiry live updates: Former sub-postmaster Alan Bates to give evidence

We’ve been hearing about the unexplained shortfalls sub-postmasters and mistresses were experiencing – but what actually went wrong with the Horizon IT system?

It’s the responsibility of those running Post Office branches to balance their accounts, which had previously been done on paper, but in 1999, Fujitsu’s Horizon was introduced.

Almost immediately there was an increase in the number of staff experiencing accounting shortfalls which they could not explain.

Josephine Hamilton, a former sub-postmistress from South Warnborough, who was convicted of fraud, says she saw the amount “double before her eyes” while using the software.

Josephine said at first the Horizon system showed there was £2,000 missing. She then contacted the Post Office support, who advised her, but after following their instructions, the amount doubled to £4,000.

Many reported that the Horizon system made it look like money was missing when it wasn’t.

Jason Coyne, an IT expert, was instructed to examine the computer system in 2003 and reported “concerning discrepancies”.

Coyne said there “was clearly defective elements of its hardware, software and interfaces, and the majority of errors noticed in the fault logs could not be attributed to the sub-postmaster”.

Coyne said the Post Office data was “unreliable” but he was ignored, sacked, and then discredited.