When Lee and Lisa Castleton bought a local post office branch in 2003, both thought it was the start of an idyllic new family life.

The business, housed in a 19th century cottage, which would also be their living quarters, was on the seafront in the picturesque seaside town of Bridlington in East Yorkshire. Both felt passionately that it was a wonderful environment in which to raise their two children. ‘It gave us every little piece of what we wanted,’ is how 54-year-old Lee puts it.

Certainly, neither of them remotely imagined how swiftly, and to what a grotesque extent, that one decision would plunge them into a nightmare in which they are still embroiled 20 years later.

For within just a few months, the Castletons would face accusations of fraud that would eventually cost them their livelihood, their home, their reputation and their health.

It would take years for them to learn that they were not alone, but just one of many hundreds of families falsely accused of theft by the Post Office in what is now known as one of the greatest miscarriages of justice in British legal history.

Lee and Lisa Castleton, pictured here with their children CJ and Millie at their daughter’s graduation. The family were put through a grotesque ordeal when the Castletons were the victims of a computer system error which the Post Office said meant they owed thousands of pounds

The couple are portrayed by Amy Nuttall (third left) and Will Mellor (fourth left) in a new ITV drama

In fact, between 1991 and 2015, nearly 800 innocent subpostmasters and postmistresses were wrongly accused of accounting errors that were actually down to a defective IT system called Horizon. Relying on IT evidence alone, the Post Office pursued them for money it said they owed, and prosecuted them if they failed to reimburse it from their savings. Many hundreds were convicted – some were even imprisoned – and lives were irreparably damaged.

Now the story has been turned into a new four-part ITV drama – starring Toby Jones, with Will Mellor and Amy Nuttall playing Lee and Lisa – which shows the scandal’s devastating impact and how families like the Castletons first faced financial disaster and then risked everything in their quest for justice.

It is a surreal turn of events for the Castletons, a self-confessed ordinary couple who only ever wanted a settled family life. ‘It is bizarre seeing what we went through brought to life like this,’ says Lee when we meet at the couple’s two-bedroom bungalow in Scarborough. ‘What happened to us still feels unreal.’

Its legacy is all too evident however: it has taken many hardscrabble years for the couple to get back on their feet, and they are very far from the life they once dreamed of.

Lee works nightshifts in a local factory to help make ends meet, while Lisa has a job in the small supermarket owned by her family. The couple, who were once mortgage-free aged 35, now have a new mortgage that will not be paid off until they are 70.

Yet it is also a long way from where they were in the midst of the scandal: at one point, they were in such penury they could not afford to heat their home and were so worried about their situation, they feared their children, Millie, now 28, and 26-year-old Cameron (known as CJ), would be taken away from them.

Branded thieves by the local community and with no obvious way of clawing back the money they’d lost or their reputation, Lee is not too proud to say that there were occasions when he stood at the edge of the cliffs that dominate the local coastline and pondered stepping off.

Only thoughts of his family stopped him. ‘Looking back, I don’t even know how we survived really,’ he says. ‘I don’t mean monetarily. I mean, literally how we got through it. It changed our lives completely. It was devastating.’

All of this leaves its mark. Lee’s raw emotion breaks through frequently during our interview, while Lisa, more self-contained, simmers with an unspoken but visceral anger. ‘We’ll never get the time back we lost to this,’ she says.

Lee and Lisa Castleton (pictured) thought they were about to start living an idyllic life when they bought a Post Office in Bridlington, East Yorkshire. But their dream would soon become a nightmare

The couple, pictured here on their wedding day, had seeked a change in career after extensive travel began to take its toll. But a years-long battle with the Post Office would make things worse

A former aircraft electrical engineer turned trainee stockbroker, Lee married former nursery nurse Lisa in 1991. Millie and CJ came along soon after. By the early noughties, with Lee’s extensive travel for work beginning to take its toll, the couple made the decision to buy the Bridlington post office. As they were mortgage free, they used the proceeds of their house sale to partly cover the £300,000 cost of their new house and business, taking out a mortgage for the rest.

After moving in in July 2003 – their children then aged eight and six – they settled in quickly, with Lee overseeing the post office, assisted by a member of staff retained from the previous owners, and Lisa running the accompanying newsagents. For the first few months all went smoothly. Then, at Christmas that year, Lee noticed he had an imbalance of £1,103.18 over a one-week period on the Horizon accounting system that he had inherited.

‘It was really odd, as we’d never had anything like that,’ he recalls. ‘We’d gone over and over all these figures, and I ended up putting that money in, which is what the contract says you must do.’

He assumed it was a blip, but the books didn’t balance over the next 12 weeks either, meaning their perceived ‘debt’ was building up fast. A baffled Lee and his assistant endlessly telephoned the Post Office IT helpline asking for help.

‘We rang all the time during that period, 91 times in all, but we were just getting passed around,’ he says. ‘We also could never establish if there were issues before we arrived, although the software was continually being updated.’

Several weeks in, and now frustrated and anxious, Lee requested an official audit from the Post Office in a bid to get to the bottom of the issue. This took place on March 23, 2004 and was, as Lee puts it now ‘the moment our lives turned upside down’.

At the day’s conclusion, the Post Office auditor, Helen Rose, confirmed they owed £25,000. ‘As only I had access to the money, the implication was that I had taken it,’ Lee says.

It was a huge sum (around £41,000 today) but, even so, Lee did not believe the problem was insurmountable. ‘I knew I hadn’t done anything wrong,’ he says. ‘I just thought that someone at their end would investigate further and confirm it was their error.’

Instead, Lee was suspended instantly, and someone else was brought in to run the sub-branch.

Not long after, after refusing to pay back the £25,000 – adamant he was not going to give back money he didn’t owe – he was dismissed altogether and taken to court by the Post Office to recoup the loss.

That decision set in motion a catastrophic chain of events. When the Post Office legal team failed to show up for the initial hearing in Scarborough, judgment was made in Lee’s favour. Yet the Post Office was determined to overturn that ruling, and took Lee to the High Court.

With no income and little in the way of savings, Lee had no option but to represent himself. He spent every waking hour ‘buried in paperwork’, working late into the night to try to establish what could possibly have gone wrong, stymied by the fact that not all transactions were available to him as only the Post Office had some of the dates. At 5.30am, both he and Lisa would get up to handle their paper rounds. ‘We were exhausted,’ she says.

In the tight-knit local community, meanwhile, rumours were spreading fast. ‘There were whispers everywhere we went,’ says Lisa. ‘Some said things to our face, like we’d taken people’s pensions.’ Lee adds: ‘We were called thieving b******s more than once.’

Such was the all-encompassing stress that Lee started to have regular blackouts, while Lisa developed epilepsy which meant that ultimately her driving licence was revoked. ‘The kids were small, and I couldn’t even drive them to school,’ she says.

Millie was so relentlessly bullied at school – including being spat at on the school bus and assaulted – that both she and her brother had to move schools. Millie went on to develop an eating disorder which would ultimately leave her regularly hospitalised.

The Castletons, pictured here on holiday, were ostracised by their community after the false allegations were made public

At this point, all of Lee and Lisa’s hopes were pinned on the High Court hearing which, they believed, would clear their name. ‘I believed they were going to say they had made a mistake,’ Lee recalls.

But on the contrary: Helen Rose, who worked as an auditor for the Post Office between 1999 and 2004, provided a witness statement to the court saying Lee smelled of alcohol, that the safe was frequently left open outside business hours, and that the subsequent owner of the post office had had no issues with the accounting system. ‘All lies,’ Lee says. ‘The safe is on a timer, so it can’t have been open, and there were errors after we left, too. But they needed to show that I was incompetent, and that is how they did it.’

Rose’s statement has since been scrutinised at the current ongoing public inquiry into the Horizon scandal. Asked why she’d signed it when she knew it contained material that was wrong, Ms Rose replied: ‘I can’t recall.’

Either way, the outcome was the worst possible for the Castletons: the court found against them and the Post Office pursued them for legal costs of £321,000.

They now know from the public inquiry that the Post Office was trying to make an example of them. Earlier this month, Stephen Dilley, who represented the Post Office in its claim against Lee, told the inquiry that the corporation knew he would not be able to pay if he lost, but that it wanted to ‘show the world’ it would defend its system.

‘So in effect, they were using me as a deterrent,’ says Lee.

It was certainly devastating for the couple, who were left with no choice but to file for bankruptcy, by now so broke they had to borrow the £800 administrative fee.

Unable to keep the newsagents open as they could no longer buy stock, they also built up mortgage arrears of £40,000 on a property that was no longer a business and therefore not worth the amount of money they had paid for it.

‘Every bill was just piling up. We were just drowning,’ says Lee, his voice breaking as he recalls the couple’s fears that Social Services would intervene and take away their children. ‘It felt like everything was against us and there was no way out.’

From the start, Lee had been convinced he could not be alone, yet despite hours ringing post office owners to try to find others in the same position, he never succeeded in identifying anyone.

‘What I know now is that people were putting money in and not really saying anything, because they were worried about losing their businesses,’ he says.

Then, in 2008, there was what Lee calls a ‘ray of light’: the Mail featured the story of Jo Hamilton, a former subpostmaster from South Warnborough in Hampshire, who stood accused of stealing £36,000. Villagers had clubbed together to raise the money but, terrified of going to prison, the mother of two pleaded guilty to false accounting.

Her conviction has since been overturned and documents uncovered by BBC’s Panorama revealed that the Post Office knew she had never stolen any money.

Horrifying though her story was, it proved to be a turning point, bringing together victims – among them Alan Bates (played in the ITV drama by Toby Jones), a prime mover in the campaign for justice in whose name the subsequent group litigation brought against the Post Office was made.

Lee recalls the first meeting of nine of them in September 2009 as a transformative experience. ‘Even though we were still in dire straits, it was wonderful to see and speak to other people with very similar issues,’ he says.

It would take many grinding years of work before their group action – by now 555-strong – was able to take the Post Office to the High Court in 2016.

The following year, a judge ruled that the Horizon computer system contained ‘bugs, errors and defects’, and the Post Office agreed to settle with all 555 claimants who joined the group litigation order (GLO). Along with the other eight original claimants, the Castletons received a settlement pay-out, although, after their bankruptcy and other debts were taken into account, they received just £30,000. Indeed, just before Christmas, it emerged that the Post Office had cut the size of its compensation pot by half, to £244 million, down from £487 million the previous year.

The Castletons’ plight, along with other subpostmasters, has been made the focus of a new ITV series called Mr Bates vs The Post Office. Pictured: Toby Jones with other members of the cast in a promotional image for the programme

Alan Bates, pictured, was a prime mover in the campaign for justice in whose name the subsequent group litigation brought against the Post Office was made

By the time the Castletons were compensated, the couple had got back on their feet through what Lee calls ‘sheer bloody hard work’, but ‘we are nowhere near where we thought we would be at this age’, he points out.

One of the things that has made them angriest has been the impact on CJ, who is a heating engineer and Millie, a teacher.

‘CJ won’t talk about it at all,’ says Lisa. ‘He says it’s ruined too much of his life already. Millie still struggles with what happened and her life was blighted for many years.’

It is only latterly, in fact, that they have discovered the extent of the damage to Millie, who, in a heart-breaking witness statement given to the public inquiry, wrote of the isolation she felt, and the all-encompassing grip the accusations had on her family. ‘Every part of my late childhood and teens was tainted by the Post Office case,’ she wrote.

It was so distressing for her parents that Lee confides he could not bring himself to read it in full, although he says that learning of the extent of her bullying left him in despair at what he calls his ‘abject failure’ to protect her.

Nonetheless, both he and Lisa are grateful for the meticulous work of the inquiry, which spent two weeks on their case alone, and further exposed the Post Office’s heinous attempts to obfuscate the extent of the technology crisis.

‘During my initial court case, I had repeatedly asked during disclosure whether anyone else was having issues and to have access to other call logs,’ says Lee. ‘At the recent inquiry, Stephen Dilley claimed that the reason they didn’t send them was because they didn’t want to ‘swamp me’ with what it turned out was 15,000 calls when, of course, they didn’t because it would expose the fact that many other people were having issues when they were trying to make out it was me alone.’

Last month, Paul Marshall, one of the barristers who is representing Post Office operators in their continuing fight for compensation, said he believed that enough evidence had emerged for police to consider prosecuting former Post Office executives.

Whatever happens, neither of the Castletons expect an apology, and say it would be meaningless even if it ever came.

‘It can’t bring back the last 20 years or undo the damage it did,’ says Lee.

Nor, indeed, the fact that mud still sticks, all these years later.

‘Even now, if both of us were to walk around Bridlington, there are looks, and certain people that say things like, ‘I bet you’re all right now,’ ‘ says Lisa.

It is why, for the Castletons, this grim and lengthy episode is far from over. ‘We haven’t got to the end of this; I’m still fighting, we’re still victims,’ says Lee. ‘But I look forward to the day when it is not the last thing I think about at night and the first thing I think about when I wake up.’

• Mr Bates vs The Post Office continues on ITV1 tonight, and January 3 and 4, at 9pm, and is available on ITVX.