What’s the biggest challenge that British business will face in the next decade? The competitive threat of India and China? Recession? Another series of The Apprentice starring Alan Sugar? Each of my colleagues in the Times business team has come up with a different answer, but, intriguingly, no one cited the problem high-lighted by a spattering of recent reports: mental ill-health.

The definition of what counts as mental illness varies in the studies, with the terms stress, anxiety and depression used almost interchangeably. Estimates of the size of the problem also vary, with reports claiming that “nearly three employees in ten have a mental health problem in any year”, that “depression is estimated to affect as many as one in five people at some point during their lives”, and that “one in four people in the UK will experience some kind of mental ill-health in the course of one year”. But what is clear is that mental illness is a major headache for employers, and will become an even bigger one.

Workplace “stress” is now the second-biggest occupational health problem in the UK after musculoskeletal conditions and, according to a World Health Organisation report, “depression” is the fourth most significant cause of suffering and disability after heart disease, cancer and traffic accidents. By 2020 it will rank second, behind heart disease. It’s no surprise that calculations vary as to what this might cost British business in lost productivity. Different reports have put the annual cost at £3 billion, £9 billion and a massive £32 billion. But the extent of the problem is perhaps best illustrated by the fact that in 2006, BT admitted that it had about 500 people off sick with psychiatric problems every single day.

What’s going on? In many ways our lives and careers are more comfortable than ever. Unemployment, the Government keeps on telling us, is very low. Most of us don’t work down tin mines but in shiny, air-conditioned shops and offices. Foreign holidays have never been more obtainable, social networking sites tell us that we have hundreds of friends apiece and we can get the complete series 1-6 box set of The Sopranos for just £49. Yet we still appear to be on the brink of an epidemic of madness and misery.

Unfortunately, no amount of staring at the evidence produces a clear explanation. The only shapes possible to distinguish amid the fog of data and commentary are the outlines of four emerging viewpoints, the first of which is that mental ill-health is increasing because modern life really is stressful, anxiety-inducing and depressing. Of course, there are many wonderful things about 21st-century Britain, but unhappiness and pain aren’t relative, and things are far from perfect. We Brits work the longest hours in Europe. There is no longer such a thing as a job for life. Many of us face the prospect of toiling for decades, barely managing to pay off telephone-number mortgages, only to find ourselves trying to live on worthless pensions and being ignored by a society obsessed with youth. And while technology may have, theoretically, brought us closer together, it has, paradoxically, isolated us at the same time, because contact has become more superficial and no one actually comes to visit any more.

This view that life is miserable and difficult was prevalent in newspaper coverage of government figures revealed last month which found that more than 100,000 young adults have been out of work on sick benefit for five years or more, largely because of mental problems. Sue Christoforou of Mind, the mental health charity, was quoted in The Times as saying that society was faster paced, the workplace more competitive and that there were more short-term contracts, “which all placed extra stress on workers”.

Meanwhile, Paul Bivand, a welfare-to-work expert at Inclusion, a think-tank, talked about “ingrained hopelessness”. But the argument is perhaps best articulated by the British psychologist Dorothy Rowe, renowned author of the worldwide bestseller Depression: The Way Out of Your Prison, who says: “Life is now infinitely better than it used to be, but we expect too much. People think they must have wonderful clothes, an interesting job and magnificent sex to be happy. There is huge pressure to be cheerful and successful, so people can become deeply disappointed with their lives. They are waiting to become famous or expect a marriage to make them happy and it doesn’t always happen.”

Which brings us to the second emerging viewpoint on the trend of accelerating misery and madness: mental illness, and depression in particular, is being overdiagnosed by the medical profession. You see, Dorothy Rowe, while acknowledging increasing disillusionment, is actually a long-established critic of establishment psychiatry, and has argued that depression is medically diagnosed for many people when they are in fact just unhappy. “The terms ‘depressed’ and ‘depression’ are applied to any dysphoric feeling such as unhappiness, disappointment, lack of enthusiasm, even irritability.”

She is not alone in the view. In a recently published book, The Loss of Sadness: How Psychiatry Transformed Normal Sorrow into Depressive Disorder, the psychiatrists Allan Horwitz and Jerome Wakefield suggest that doctors are transforming sadness – a natural human emotion – into a disease. They argue that the definition of the condition is too narrow – diagnosis requires only the appearance of symptoms such as insomnia, change in appetite and fatigue – and that, as a result, all clinical approaches to the condition are flawed. There is a big difference, they say, between someone who becomes sad because of a relationship or career failure and people who feel sad for no reason: it’s only the latter whose brain chemistry is malfunctioning and requires medical treatment, but medicine tends to treat both.

It doesn’t take a huge amount of imaginative effort to extend this scepticism to other mental health conditions when you realise that, in recent decades, psychiatric diagnosis has expanded so much that there are now some 300 disorders defined inThe Diagnostic and Statistical Manual of Mental Disorders, the bible of the psychiatric profession, and when guides on mental health claim that so much basic human behaviour is indicative of psychiatric distress. Here’s a list of symptoms that one such diagnostic manual cites as potential indicators of mental ill-health: “inappropriate or exaggerated responses to situations; excessive restlessness; drowsiness; worrying excessively; reduced confidence; mood swings; indecisiveness; poor concentration; trembling, sweating; lethargy; social withdrawal; irritability or anger; intoxication; dramatic weight loss or gain; change in personal hygiene or dress; feeling helpless or hopeless; being isolated; threatening or dangerous behaviour; bizarre behaviour or thinking”.

Is there anyone who doesn’t experience several of these symptoms during the average working week? I think I’ve experienced most of them during the writing of this piece.

And, of course, it is such scepticism which leads to the popular view that mental illness is only “increasing” because there is no scientific test that can prove it and it is therefore an easy way for malingerers to evade work. You don’t need to search hard to find articulations of this viewpoint. You can sense it in the tone of the news coverage of last month’s benefit figures, in promises from politicians to tackle the problem by getting people from welfare back into work, and was voiced loudly in the Daily Mail’s leading article on the subject recently: “Some will be genuinely ill and deserve the fullest sympathy,” railed the paper. “But it is inconceivable that so many could be incapable of seeking work in the prime of their lives. What we have is not a sickening society but one which is becoming institutionally indolent.”

If this harrumph were allowed to continue, it would doubtless go on to say that our grandparents’ generation was never so lazy and soft: they were just thankful the bombs had stopped dropping on their heads, and worked because they were proud to do so and because they wanted to feed their starving children.

And here we have what I think is a fourth popular view on the subject, that mental illness is “increasing” only because the stigma of it has eroded. In short, people are no longer ashamed of confessing to psychiatric difficulties, and are more likely to seek help.

Of course, there remain spheres of working life where confessing to stress, depression or anxiety is still taboo: in politics, for instance, and in the City of London. Lord Stevenson of Coddenham, the chairman of HBOS, one of the biggest banks in the world, made headlines last October when he spoke candidly about his experience of clinical depression. Chairing a conference in Glasgow on mental wellbeing, he admitted that he had a significant episode 12 years ago, had recovered, but now referred to the condition as “the bug” – because it was inexplicable as an infection or virus. Meanwhile, Jonathan Naess, a City banker, has just launched Stand to Reason, a charity that aims to combat the stigma of mental illness in the Square Mile.

But elsewhere, and in the media in particular, admitting to mental illness is no longer so rare. Stephen Fry recently won plaudits for his frank documentary seriesThe Secret Life of the Manic Depressive, Alastair Campbell has talked about his struggle with the blues, and the writer Stephanie Merritt has just written a moving book about her depression. Merritt wrote a piece on the subject recently for The Observer which began with the claim that depression remains “largely taboo”, but then proceeded to mention that two other books on the same theme, also by women journalists, were being published at the same time. And then, in the same edition of the same newspaper, there was an interview with Meg Matthews, interior designer and former girlfriend of Noel Gallagher, who was quoted remarking: “I hit my 40th birthday in 2006 and I got depressed. I was drinking and not feeling happy. Nothing excited me. I told my GP and he recommended rehab.”

It is perhaps no surprise that employers, who have to shoulder the burden of absence, worry that such confessions show that psychiatric distress is being admitted too easily and that people should just get a grip. You won’t hear many saying this out loud, presumably out of fear of upsetting those with genuine and serious problems, but their views become clear in surveys. Nearly three quarters of 550 British businesses recently surveyed by the mental health charity Shaw Trust estimated that only as many as 5 per cent of employees suffered from a mental health problem at any point in their working lives, while almost half suggested that none of their employees would – estimates that clash with the frequently quoted statistic that one in four people experience stress, anxiety, depression and other forms of mental health in any given year.

Moreover, many employers don’t believe that doctors are doing enough to get the “mentally ill” back to work. According to a survey of more than 600 employers conducted by the Chartered Institute of Personnel and Development, and the professional services firm KPMG, most would like sick notes to include more information on “return-to-work possibilities”, employment advisers placed in surgeries, incentives to be included in GP contracts encouraging doctors to work more closely with their patients’ employers; and better training for GPs on “fitness-to-work issues”.

However, not all employers take such a jaundiced view, and one that doesn’t is BT. It has adopted the first position, that mental ill-health is increasing simply because modern life is difficult, and believes that cynicism is dangerous even if there is an element of fakery and emotional diarrhoea because it could lead to people with serious problems not being given the support and sympathy that they deserve. Indeed, the list of symptoms from the aforementioned diagnostic “manual” is actually taken from a document entitled Open Minds: a Guide to Mental Wellbeing at BT, which aims to help line managers to identify mental illness in staff. It was introduced as part of BT’s Work Fit – Positive Mentality awareness programme, which formed part of several initiatives launched in 2002 when the company realised that its sickness rate was above average and increasing.

The programme was developed in collaboration with various trade unions and mental health charities and has three strands: prevention, intervention and support.

“Prevention” involves BT line managers talking to staff to spot early signs of stress, regularly monitoring how staff are feeling, developing a workplace culture in which people feel comfortable talking about mental health and offering employees information on how regular exercise and relaxation techniques can help ward off depression, stress and anxiety.

“Intervention” involves managers getting involved early to abort problems, identifying hotspots of stress and problems with individual employees. “If someone is crying for no reason, the human reaction is to ask if they are OK,” says Paul Litchfield, BT’s group chief medical officer. “But surprisingly, particularly in the UK, it doesn’t seem to happen very often.”

The third stage – support – involves the implementation of radical policies aimed at trying to get the sick back to work once they are off. BT line managers are expected to keep in touch with staff when they’re sick. And if someone is off for a significant period, the rehabilitation plan involves getting people back to work initially on a reduced-hour basis, looking at aspects of their job that are particularly pressured and rearranging responsibilities, adjusting the content of their job to maybe half the load, allowing time off for attending therapeutic sessions, changing shift patterns, allowing a later or earlier start to avoid rush-hour travel, and offering a quiet place for staff to go to if they feel anxious or stressed.

If this all sounds a bit soft and indulgent, it is worth looking at the results that BT has achieved. In 2002 sickness absence was running at 3.6 per cent. It now stands at 2.4 per cent. Over five years, mental health sickness has been cut by 30 per cent and the medical retirement rate for mental illness by 80 per cent. Seventy-five per cent of long-term absentees, for both physical and mental health, now return to their job – the national figure is 20-25 per cent, while BT’s rate used to be 30 per cent.

Work-related cases of ill health, of which about 40 per cent are due to stress and mental illness, have fallen by 64 per cent. “When you talk to people you have helped back into work after a mental illness, they always say they are working better than ever,” Litchfield adds. “And they are always incredibly positive about the company. If you give someone a helping hand at a time of crisis, they will think well of you for ever, and repay you with incredible loyality.”

Where to find help

Mind Offers a helpline, drop-in centres, supported housing and counselling: 0845 7660163; www.mind.org.uk

Rethink Support and advice for everyone affected by severe mental illness: 020-8974 6814; www.rethink.org

Sane Offers information, crisis care and emotional support: 0845 7678000; www.sane.org.uk