It is known in medical circles as the Oscar Pistorius question: if an athlete with no legs can compete at Olympic level, why should an employee with a history of mental illness not be allowed the chance of holding down a decently paid job?

Richard Saville-Smith is posing precisely this question at an industrial hearing in Edinburgh, where he claims that he was dismissed from his high-powered public relations job with Scotland’s tourist agency, despite a track record of achievement at executive level, because of an onset of bipolar disease, or manic depression.

The case is continuing, and the facts have not yet been established. But it is an important test not just of discrimination law, but of civilised values. There is no justification for bias these days against those who carry the burden and the stigma of mental illness.

Indeed the law forbids it. The Disability Discrimination Act specifically protects job applicants or employees from discrimination on the ground of serious mental impairment up to and including schizophrenia. The European Convention on Human Rights included it as recently as this year: no personnel office is unaware of the implications.

And yet the very phrase mental illness makes employers shrink. For all that we have learnt about the causes of mental illness, its likely course, and the ways it can be controlled, it remains one of the great taboos of society. It is seen as hard to predict, unstable, unreliable: qualities that do not encourage confidence in a future employer.

Unlike Pistorius, whose disability is hard to ignore, that streak of depression that hits you from time to time, or the bipolar episode that haunts you from the past, cannot be seen, defined or predicted. The Act deliberately refrains from offering a definition of mental impairment, and leaves it to the judgment of the individual, GP or employer to gauge its seriousness.

And so, if you are applying for a job, every instinct tells you to suppress all reference to the counselling you may have briefly had as a student, or the time when you were prescribed antidepressants to take you through a rough patch in your life. You know, and who is to gainsay it, that if you are just one of a dozen applicants for the post, that minor revelation, however buried in the past, is likely to be the element that flips your application on to the reject pile. No one will be able to prove that was why you were turned down, so any appeal is doomed.

So you decide to omit it. Yet, even as you do so, you know that if your little deception is found out, that really will finish your prospects. Attempting to demonstrate your sanity by airbrushing out any reference to a previous illness may well rebound against you. If the omission is detected, it will be seen, not just as a minor suppression, but as a failed attempt to conceal something really serious — your own insanity. Mental illness may be a drawback, but lying is terminal.

No one pretends that the decision is easy. The police, for instance, have to be aware of their responsibilities to the public — no one is going to be particularly impressed if an armed response team includes an officer prone to bouts of manic depression. But approaches vary from force to force. At Scotland Yard, all applicants have to fill in a medical questionnaire that asks specifically if they have any history of mental illness. They may then be called in for a medical assessment, and are judged case by case. At Lothian and Borders Police in Edinburgh, no past history is taken into account, but anyone suffering from a current mental illness is unlikely to be considered for an officer’s job.

“Employers are nervous about mental illness, of course they are,” said one expert I spoke to. “But it is not as threatening as they think. We need to educate them more.”

This is not just a moral dilemma for a small minority. A World Bank international study of mental illness in 2000 found that it was second to heart disease as the greatest disability among employees. By 2020 it is expected to have reached No 1. Dealing with it is no longer a marginal concern.

Yet, understanding mental illness does not require a journey into an unknown world. As anyone with first-hand knowledge of it is acutely aware, what may seem a permanent condition to some is often nothing of the sort. It may, like a bout of flu, be treatable in days. It may linger for years and yet be well controlled by a chemical regime that is enough to suppress its more extreme symptoms. It may, from time to time, require a period of absence, but be matched by long bouts of well-balanced behaviour.

And the compensations make any minor inconvenience more than worthwhile — for it is frequently the most creative, imaginative and inspiring of colleagues who suffer from bouts of depression or even a bipolar condition that may, from time to time, take a more serious form.

By turning our backs on those who do not easily conform to our notions of the conventional, we are excluding those who may well surprise us by their innovation. And that is not just a bias against mental illness, it is a bias against achievement.

Times Recommends

• Caesar & Cicero: Balls & Mandelson
• The anti-sex brigade are the worst
• Small act of charity won’t change the world