I had tried to prepare myself mentally, but I had no bag. I wasn’t suitably dressed: I was in a suit. And now I was locked in a tiny cubicle, being hurled from side to side as the van lurched around corners. I felt sick, both physically and psychologically.

‘If you treated animals the way we treat prisoners on their way to jail, animal rights groups would be incensed. And this was only the beginning.’

Consultant surgeon David Sellu is describing the worst day of his life – November 5, 2013 – when he was transported to Belmarsh in London, one of Britain’s toughest high-security jails, to start a two-and-a-half-year sentence for killing a patient in his care.

David Sellu (pictured with his wife Catherine) was convicted of manslaughter in 2013 over the death his patient James Hughes and sentenced to two-and-a-half years in prison

His exemplary 40-year career, his professional and social standing, his family’s financial security – all were wiped out by the Old Bailey jury’s verdict that Mr Sellu was guilty of gross negligence manslaughter in causing the death of James Hughes, 66.

Last week, 16 months after this newspaper exposed how vital evidence that might have cleared Mr Sellu was hidden from his trial, the Court of Appeal quashed his conviction. But the damage is done. His career is in tatters. His reputation ruined. And the ‘totally degrading’ trauma of being locked up 22 hours a day in a jail containing rapists and murderers has taken a heavy toll.

His story is a shocking indictment of the ‘blame culture’ afflicting Britain’s hospitals, which is seeing increasing numbers of healthcare workers thrown to the legal wolves – with potentially devastating consequences for patients. It also chillingly illustrates how easy it is for a public-spirited professional to find himself on the wrong side of the law.

‘I feel no jubilation, only a little relief,’ says Mr Sellu, 69, speaking exclusively to The Mail on Sunday at his West London home. Courteous and softly spoken as he recalls his long ordeal, he shudders, occasionally rubbing his eyes to hide his tears.

‘I still can’t sleep properly. I’m on beta-blockers to stop my heart racing. And I feel like a pariah. I’ve had to cope with headlines that called me “Doctor Death” and “Killer Surgeon”. That doesn’t go away. The Crown Prosecution Service knows they made a hash of this case. My hope now is that they will think twice before trying to criminalise others working in healthcare.’

Mr Sellu’s journey to the top of Britain’s medical profession began in a poor village in Sierra Leone. He is the eldest of ten children, born to rice-farmer parents who had no education. His chance came when his slightly wealthier aunt, who lived in Bo, the nearest town, offered to pay for him to go to school there and put him up.

‘It was an excellent school and I got good grades. Eventually, I won a national scholarship to study in England,’ Mr Sellu says. He entered Manchester University medical school in 1968.

Once he qualified, his progress was assured. He took up successive posts in Manchester, London and Southampton. In 1981, he married Catherine, an intensive care nurse he met at Hammersmith Hospital in London. The couple have four children.

Mr Sellu worked for the Clementine Churchill in Harrow, owned by healthcare giant BMI. A damning report, which might have cleared the surgeon was hidden by senior BMI staff

Mr Sellu’s reputation as a meticulous, unflappable surgeon steadily grew, and in 1993 he was headhunted to become an NHS colorectal consultant at Ealing Hospital. Later he also worked part-time at the private hospital where Mr Hughes died – the Clementine Churchill in Harrow, owned by healthcare giant BMI. He has also spent months as a volunteer surgeon in the country of his birth.

When the police started investigating Mr Sellu, they combed through his record, searching for evidence that the death rate among his patients was abnormally high. There was none, and many colleagues gave glowing testimonials about his skill and experience.

Mr Sellu first saw Mr Hughes – a building firm boss from Northern Ireland – on February 11, 2010. Five days earlier, Mr Hughes had been given a replacement knee, but had developed worsening pain in his abdomen. Mr Sellu agreed to see him as a favour to the surgeon who did the knee op – largely because, at a private hospital at night, there was no one else, other than the more junior resident medical officer. The junior doctor thought Mr Hughes had cramp, and had given him muscle relaxants. Mr Hughes was in agony: clearly they were not working.

In fact, Mr Hughes had a perforated bowel – a life-threatening condition. But Mr Sellu was not able to operate until the early hours of February 13. By this time, Mr Hughes was critical, and never recovered consciousness. ‘I’m still very sorry for his family,’ Mr Sellu says. ‘They lost a husband and a father. I’ve analysed what happened a thousand times, and with the benefit of hindsight, there are things I might do differently. But there were reasons for the delay in operating that had absolutely nothing to do with me – for example, there was no rota for emergency anaesthetists.’

It was not until after Mr Sellu was convicted that the hospital sent an email to its doctors suggesting a rota be formed.

An inquest into Mr Hughes’s death opened in October 2010, but the coroner quickly halted it, and ordered police to begin a criminal investigation of Mr Sellu.

The consultant found himself being interrogated hour after hour, being asked repeatedly about the tiniest details of the case. ‘They were looking for discrepancies, trying to trip me up, so they could say I was a liar,’ Mr Sellu says. ‘They had a crime and a suspect, and they were trying to prove their case.’

But as this newspaper revealed last year, all this time a crucial document was hidden: a secret report by senior BMI staff compiled after Mr Hughes’s death. This so-called ‘root cause analysis’ found there were ‘inadequate’ procedures at the hospital when routine cases became emergencies, delays in getting scans, X-rays and an anaesthetist, and a failure to monitor Mr Hughes’s condition.

After his trial, November 5, 2013 Mr Sullu was transported to Belmarsh in London, one of Britain’s toughest high-security jails

Mr Sellu was charged with manslaughter. He could no longer work, even in the NHS. ‘Imagine, you’ve been working all your life, and suddenly your salary is stopped, and you’re told you may have committed a criminal act,’ he says.

In 2012, his six-week trial began. The secret report was never shown to the jury. According to the prosecution, Mr Hughes died because of Mr Sellu’s ‘laid-back’ attitude. The jury deliberated for more than three days. When it came to sentencing, Mr Sellu says: ‘I felt the handcuffs go on my wrist. I looked up at my family. There was a lot of sobbing, but they were trying to make encouraging gestures.

‘I was taken down to the cells, and my barrister gave me a pep talk, saying I had nothing to worry about and would soon be in an open prison. And then they took me to Belmarsh.’ There was further humiliation to come: a long wait to be processed, and a strip search. ‘It was totally degrading,’ admits Mr Sellu.

Finally, he was taken to a cell with three other prisoners and two sets of bunks, with almost no space between them. The shared toilet was open – ‘the stench was the first thing I noticed’ – and they were locked in the cell for 22 hours a day.

Mr Sellu says: ‘I was trying to stay strong because my family were going through hell too. But I was on the top bunk, freezing, with one tiny blanket. The bed was very narrow, and every movement by the guy on the bottom bed was magnified. I barely slept at all.

‘Throughout my career I made life-and-death decisions, and now every aspect of my life – when I could wash, what I could eat – was controlled by someone else. I was terrified. I had been warned not to let other inmates know I was a doctor, because they might have assumed I was some kind of Harold Shipman [the serial-killer GP who murdered more than 200 patients] and sought retribution.

‘I was in a tiny space with three strangers, with one panic button by the door. My family could not send books. All I could do 22 hours a day was sit on my bunk, legs dangling, or try to sleep.’

Last week, the Court of Appeal said the trial judge failed to tell the jury how only truly exceptional negligence could rank as manslaughter. Cases of healthcare workers being accused of criminal conduct are increasing, with at least three convicted in the past two years

After a month, Mr Sellu was moved to Highpoint, a high-security jail in Suffolk, where conditions were better, and finally, in the months before his eventual release in 2015, to an open prison. He served a total of 15 months. But even after being freed, his life was in limbo: ‘I felt ashamed to walk past my neighbours. And, of course, I could not work.’

Last week, the Court of Appeal said the trial judge failed to tell the jury how only truly exceptional negligence could rank as manslaughter, and how they might determine whether this had occurred. Yet cases of healthcare workers being accused of criminal conduct are increasing, with at least three convicted in the past two years.

Mr Sellu says two things helped lift his morale after being convicted. One was this newspaper’s investigation, and the other was a campaign chaired by his Ealing colleague Jenny Vaughan, a consultant neurologist. Dr Vaughan’s petition gathered 3,000 signatures, many from top doctors and former patients.

Dr Vaughan says: ‘Of course we are pleased with the decision. But as a doctor, I’m interested in what makes patients safer, so that lessons are learned. The threat of criminal charges only promotes cover-ups.’

Mr Sellu highlights another danger: ‘The potential consequence of my prosecution is that in cases where a patient may die, a surgeon might walk away rather than operate – because that will be safer for the doctor.

‘Some patients who might live will lose their chance of survival.’

Mr Sellu still has to face the General Medical Council. But despite his appeal victory, his desire to practise his hard-won skills has gone. ‘Sometimes I think of the patients I could have treated while I was in prison. But I don’t want to go back to surgery. I’d like to do some teaching, some writing and research.