Henry Cockburn was diagnosed with schizophrenia in 2002. Until then, his father Patrick, The Independent’s award-winning foreign correspondent, knew next to nothing about the illness. But sharing the news with his friends made him realise how many people had had the same experience but kept it secret. Today, in the third instalment of his ground-breaking four-part series, he contrasts the prevalence of mental illness with its stigmatised public perception.

When my son, Henry, was diagnosed with schizophrenia in early 2002 I knew nothing about mental illness. After seeing him for the first time in hospital in Brighton I went online in my hotel room and was dismayed to discover that the US Surgeon-General had said that schizophrenia was to mental disorders what cancer was to physical illness.

Later, I mentioned to close friends what had happened to Henry and found that a significant number knew all too much about schizophrenia because they had a close relative who suffered from it. Looking after a schizophrenic brother or a sister, or, most commonly, a son or a daughter, turned out to be a preoccupation that dominated their lives.

But these same friends had never previously mentioned their struggles with mental illness to me, though I thought I knew them well and they must have known that I was likely to be sympathetic. Some of their stories were appalling. A sister-in-law suffering from schizophrenia poured petrol over herself during a family holiday and took weeks to die from her burns; an apparently happy son at the end of his teens suddenly killed himself; loved ones had their lives ruined by voices and delusions. Accounts were grim but also uplifting, showing again and again the courage, self-sacrifice and endurance of families helping a mentally ill relative.

Why are people so secretive about mental illness – schizophrenia in particular – in a way they are not when a serious physical illness is involved? Why did my friends only speak to me about what had happened to them after Henry was diagnosed with schizophrenia, as if they could only expect sympathy and understanding from somebody similarly touched by a serious mental disorder?

There is the obvious wish to avoid stigma: a consuming fear that a son or daughter known to be schizophrenic will be shunned as an outcast, ostracised socially and unable to get a job. It is a reasonable fear since people are wary of an individual admitting to a mental disorder, though they may express sympathy for the plight of the mentally ill in general. A NHS survey on attitudes to mental illness in 2011 showed that 77 per cent of people agreed that “mental illness is an illness like any other”. But only 25 per cent agreed with the statement that “most women who were once patients in a mental hospital can be trusted as babysitters”.

Advocates for the rights of the mentally ill seek to combat discrimination, intolerance and ignorance. They see these as being fostered by a media that irresponsibly links mental illness to crime and violence, stigmatising the great majority by dwelling on the actions of a sub-group of highly psychotic or drug-abusing individuals. A report by Mind, a lobbying group for the mentally ill, says “there is a common perception that people with mental-health problems are likely to behave in a violent way – a view that is supported repeatedly by films, novels and the media”. The insane, cunning, random killer is a staple of drama in every format and this is a tradition unlikely to change.

Mentally ill people protest that they are, in fact, more likely to be the victim of an act of violence than the perpetrator, and that the great majority of murderers are sane. Of the 5,189 homicides in Britain over nine years between 1997 and 2005, only some 510, or 10 per cent, were committed by people who had been in contact with the mental health services over the previous 12 months. Somebody with schizophrenia might appear to be four or five times more likely to carry out a violent crime than the rest of the population, but studies show that the figures are skewed by a criminalised minority and that 99.97 per cent of people suffering from schizophrenia will not be convicted of serious violence in a given year.

Such statistical evidence may be compelling, but does not in practice determine popular perceptions of risk. The chances of a mentally ill person making an unprovoked attack on a stranger are tiny, but this will not comfort a public accustomed to watching terrifying fictional stereotypes of the insane as portrayed in Psycho or Silence of the Lambs. Ignorance of mental illness, and a genuine scientific bafflement over its precise mechanics, creates a vacuum of information that is filled by melodramas on television or at the cinema.

And when real killings by people with mental disorders do occur they are heavily publicised, thereby reinforcing existing fears which are shown to be not wholly illusory. One psychiatrist says, “It is not the frequency of such murders but their unpredictability that makes them scary”. Another psychiatrist I interviewed said he hoped I could do something to reduce stigma, but he also asked that on no account should his name be published because he feared being stalked by former patients.

A businessman told me that, many years earlier at the height of his full blown psychosis, “I fully intended to go to my grandparents’ home on the south coast because I believed I should kill them to preserve their innocence”.

Campaigners blame exaggerated media coverage of the mentally ill for exacerbating stigma. They quote one journalist as saying, “There is no sexiness in mental health unless someone has committed a terrible crime”.

This is correct, but the media reflects public fears and its exaggerations are scarcely new. Dramatists have been associating murder and madness in England at least since Shakespeare portrayed Lady Macbeth urging her husband to murder before going insane.

The campaign to reduce stigma has had some success, making it more difficult to portray the mentally ill as aliens from another world. But the NHS survey of attitudes to mental illness shows that opinions are slow to change. Some 62 per cent of people agreed in 1994 with the statement that “people with mental illness are far less of a danger than most people suppose” and the figure was exactly the same in 2011. The proportion saying that residents had nothing to fear from people coming into their neighbourhood to obtain mental health services rose from 62 to just 64 per cent over the same period. Perhaps another approach to reducing stigma is needed.

There is also a danger seldom mentioned that, in seeking to emphasise the humanity and normality of a mentally ill person, the catastrophic nature of schizophrenia and other serious mental illnesses is understated.