For many years, William Graham was a familiar and well-respected face in his local community.

As manager of the sub-post office located within a pharmacy in Riverhead, near Sevenoaks, his reputation was important to him.

“I enjoyed working with the local people,” he explained, “talking to customers and generally building the business up.”

In fact, he was a similar pillar of the community as that portrayed by Toby Jones in ITV’s Mr Bates vs The Post Office – an acclaimed dramatisation of a scandal so shocking it has been proclaimed one of the nation’s greatest miscarriages of justice.

But back to Mr Graham.

He had lived in Kent since he was 21, the year before he took up a job as a trainee for the Post Office. Coinciding with his new job, he met his wife – the two tying the knot in 1996 and going on to have two daughters.

As his career within the well-respected organisation continued, he went on to become an in-house training manager on a highly sophisticated piece of IT kit introduced by the Post Office to help automate book-keeping across counters nationwide.

Called Horizon, it was rolled out around 1999/2000. At the time, it is said, it was the biggest non-military IT project in Europe.

Designed to allow sub-postmasters and branch workers to key in sales on a touchscreen, Horizon would automate the accounts in the background – sending all the figures directly to Post Office headquarters.

Except, of course, it had one major flaw. It was prone to getting its sums very badly wrong.

In the summer of 2002, Mr Graham took redundancy from his Horizon training job – a move which would pave the way, a few months later, for when he was approached about the Riverhead job.

He was, after all, perfectly positioned to take the role. He had worked for the Post Office for a number of years and was well-versed with its swanky new IT system.

“It would be a long-term position,” he said. “I thought it would see me through to my retirement.”

Now in his 30s, the job would allow him to be his own boss (sub-postmasters are not direct employees of the Post Office – rather they agree a contract to run its services from certain approved premises) and provide the income to support his young family.

It all seemed to be perfect.

Yet when he stood behind that counter for the first time in November 2002, he can never have thought that within 10 years his entire life would be turned upside down due to an IT error.

He would have a criminal record – forced to admit to a crime he knew he had not committed in order to avoid jail – his reputation left in tatters and the impact on his mental health so significant he had considered taking his own life.

He was left sinking under a personal debt mountain which, at one stage, almost stole the house he had worked so hard to provide his family.

And all because of the IT system he used each and every day.

As part of the contract the Post Office had with its postmasters, if there were any shortfalls in the financial ins and outs of a branch, the postmaster would be liable.

Any discrepancies would, most frequently, be deducted from their salary. It would, the Post Office felt, ensure each postmaster was extremely careful when it came to ensuring every penny was correctly accounted for.

It didn’t take long before Mr Graham started noticing he was facing regular shortfalls.

“Initially,” he recalls, “I would report all shortfalls to the Post Office helpline. They advised me to pay the alleged shortfalls ‘centrally’, which means my salary would be deducted to take into account the alleged discrepancies.

“Alternatively, I would pay the shortfalls out of my own pocket.

“I regularly experienced initial small shortfalls and excesses, but they were all below £100.

“On some occasions I could explain them as they were the result of human error – on other occasions, I was completely baffled by them.

“The shortfalls then began to get bigger such that in 2004, for example, we had a shortfall of £5,000.

“With any shortfall, I was required by the Post Office to repay it in full. This was despite not having any explanation as to how the shortfall had occurred. This was deducted from my salary over the course of a year.

“I had to accept the figures Horizon gave me and put the cash in to satisfy the Post Office.”

But the situation was about to escalate to a previously unimaginable level.

“There was a shortfall of £50,000 in 2008. It was so large I was scared to report it. I hoped it would right itself, but it never did.”

By January 2009, auditors arrived to check his accounts. The shortfall had now grown to £65,521. The Post Office was notified and Mr Graham told not to enter the branch again. It would be the last time he ever set foot in the store.

I was scared stiff. They tried to make me say I had taken the money

He was interviewed by Post Office investigators at Bexleyheath police station, while they also searched his home.

“I was scared stiff,” he said, “they tried to get me to say I had taken the money – which I denied.”

Suspended from his job, it also meant his salary was frozen too.

A calamitous situation made worse when he was ordered to repay the shortfall – money he had to obtain by borrowing from friends and family and maxing out loans and credit cards.

By November of that year, a criminal investigation was underway.

“Before all of this,” he said, “I was a confident and widely respected member of my community.

“I lost contact with my friends and the people I used to work with after being suspended. To me, it appeared people had already made up their minds that I was guilty.”

It left him unable to sleep, prescribed anti-depressants by his GP and “in a very dark place”.

He added: “I felt guilty, although I knew I had not done anything wrong.

“I felt worthless and that I had brought shame on myself and my family.”

Appearing before Sevenoaks Magistrates in June 2009, his case was referred to Maidstone Crown Court.

When it finally went before a judge in January 2011, he was accused of false accounting and theft.

He pleaded guilty to two counts of false accounting, explaining: “I was advised that if I pleaded guilty to false accounting they would drop the theft charge. I was advised if I went this route, the chances of my receiving a custodial sentence would be reduced.”

Desperate to avoid jail, the judge accepted his guilty plea on the two counts and he was handed a 32-week suspended jail sentence and ordered to carry out 100 hours of unpaid work.

To add further salt into his already gaping financial wound, he was also told to pay the prosecution case’s legal costs of £3,589.

My feeling of worthlessness and low self-esteem worsened and I had suicidal thoughts at times

He completed the unpaid work at a local charity shop – working in a backroom in order to avoid eye contact with those who knew of his fall from grace.

He had become one of hundreds of honest, law-abiding postmasters and mistresses who had been prosecuted as a result of the Horizon accounting system.

Unable to find another job as a result of his conviction, it was not until 2014 he could come off benefits and secure a job as a medical courier.

“Following the sentence,” he revealed, “my feeling of worthlessness and low self-esteem worsened and I had suicidal thoughts at times.

“Even talking about it now is painful.

“The whole situation with the Post Office has had a significant impact on my well-being and self-confidence and has caused myself and my family so much hurt over the years.

“I lost family and friends. They stopped talking to me straight away. People in the local community did not want anything to do with me or my family.

“I was unable to take my daughters to school because I feared shame and humiliation at the school gates.”

What he was not to know, at the time, was that while the Post Office was telling each postmaster and mistress that no one else had experienced such shortfalls innocently, plenty had.

Horizon was, in fact, prone to misreporting figures.

The Criminal Cases Review Commission – the independent body which investigates potential miscarriages of justice – describes the Horizon/Post Office debacle as “the most widespread miscarriage of justice the CCRC has ever seen and represents the biggest single series of wrongful convictions in British legal history”.

It explained: “Alleged problems with the Horizon system were first reported by Computer Weekly in 2009. There were concerns that faults in the system were causing it to overstate the amount of cash or stock which should be on the premises of a particular branch.”

Yet prosecutions continued until 2015, with the Post Office dismissing any claims its system was to blame.

Computer Weekly explains: “For 15 years after the roll-out of Horizon, the Post Office – which has private investigation and prosecution powers with no need for police involvement – prosecuted more than 700 sub-postmasters for crimes such as theft and false accounting.

“Hundreds of sub-postmasters were sent to prison and many more received punishments such as being forced to do community service and having to wear electronic tags. They lived their lives with criminal records.

“Hundreds were made bankrupt, losing their livelihood, and many struggled after being forced to pay the Post Office to cover shortfalls that didn’t exist outside the Horizon system. The lives of the victims and their families were severely impacted, with several suicides linked to the scandal and many cases of illness caused by stress.”

Between 2000 and 2014, it is claimed around one sub-postmaster a week was being prosecuted for theft, false accounting and other offences, by the Post Office, as a result of the Horizon glitch.

By 2019, the Post Office had finally admitted Horizon was at fault. That same year, a group of Post Office workers won a High Court case in which their convictions were ruled wrongful.

In 2021, the High Court quashed the convictions of what would become known as the Post Office 39 – among whom was Mr Graham.

It triggered a demand for a public inquiry and justice for the many hundreds of others whose lives had been devastated by the false allegations.

“When the Court of Appeal quashed my conviction,” Mr Graham told the public inquiry into the scandal, “it felt like a big weight had been taken from my shoulders”.

In September of last year, the government confirmed that all those wrongfully convicted would be offered £600,000 in compensation.

Yet, hundreds of convictions are yet to be overturned, while there are numerous claims of compensation for those cases quashed several years ago still not being paid.

While those affected try and rebuild their lives, no-one from the Post Office – or Fujitsu, the Japanese company behind the Horizon software – has faced prosecution.

A Post Office spokesperson said: “We’re acutely aware of the human cost of the scandal an we’re doing all we can to provide redress both in respect of paying compensation and assisting the Horizon IT inquiry.”

The inquiry is expected to finally conclude and issue its findings later this year.

The fight for justice continues.

Mr Bates vs The Post Office is available to view on ITVX.