Ron Ferguson: One in five Scots either have had, are having, or will have mental illness of one kind or another. What makes life even harder for the sufferer is the stigma attached to such troubles, even in the 21st century.

When Ronald Reagan was President of the United States of America, it was memorably said of him by a White House insider that a particular crisis had given the President "many a sleepless afternoon". There immediately followed much angstful discussion about whether it was possible to feel secure when the most powerful figure in the world spent so much time sleeping, yawning, or in a dwam. I must say that I always felt much more secure when President Reagan was tucked up in bed.

Nowadays, political leaders are hardly allowed to sleep at night, never mind during the day. Nor are our leaders allowed to be depressed, as Alastair Campbell, spin doctor to the gaunt and hollow-eyed Tony Blair, has pointed out. Winston Churchill, he observed, probably wouldn't have made it to the top if he had lived in modern Britain. That sobering thought is worth reflecting on.

Mr Campbell, who is bravely open about his own battles with booze and depression, insists Churchill would most likely have been stigmatised due to his depression, which he referred to as his "black dog". Pointing out that other figures such as Florence Nightingale, Abraham Lincoln, Charles Darwin and Marie Curie had suffered from depressive illness, Mr Campbell went on: "I sometimes wonder how these great historic figures would have fared had they been alive today - Churchill with his depressions, drinking and long lie-ins, and Darwin with his severe anxiety and mental torment. I am not convinced that a modern politician who admitted to mental health problems would be able to get to the top."

Imagine if Churchill, in the 1930s, had been disqualified from high office by what is now termed "an image problem". The country would have lost the leader who was best equipped, despite his frailties, to stand up to the Nazi threat. These days we inhabit a political culture in which a macho, super-competent image - which certainly doesn't allow for depression - is deemed essential. Indeed, this culture extends well beyond politics. In a report, written for Time to Change, a new campaign mounted by leading mental health charities, Campbell wrote: "In the 21st century mental health problems are a big taboo and many of those affected find themselves sidelined, kept out of the top jobs and treated as incapable.

"Today, more than 60% of employers say they wouldn't consider employing someone with a history of mental illness. Perhaps they don't realise what talent they are missing out on. Had this discrimination applied to Churchill, Lincoln, and Nightingale we can safely say that today's world would be a very different place."

Some countries handle this issue much better than others. A few years ago, the prime minister of Norway, an ordained Lutheran pastor by the name of Kjell Magne Bondevik, announced that he was taking leave to deal with his depression. What is remarkable is the lack of fuss made about it. The media allowed the Norwegian premier to recover in peace; the opposition parties made no capital out of it. Indeed, they were sympathetic to him and wished him well. He was back at his desk, much refreshed, a month later. What a civilised way to conduct the political process. Can you imagine that happening here? Of course not. If Gordon Brown were to drop out for a few weeks because of depression, his illness would be regarded as a form of terminal weakness and he would be pilloried daily until he was forced to relinquish office. Japan's Crown Princess Masako also took some time out from her public duties to deal with a depression which was triggered by the pressure to produce a male heir to the world's oldest hereditary monarchy.

A poll accompanying the Time to Change report found that 29% of members of the public think someone with a mental health problem is unable to do a responsible job. Yet one in five Scots either have had, are having, or will have mental illness of one kind or another. We're not talking about feeling a bit low, or having a few ups and downs, but about afflictions that can range all the way from a low mood that's difficult to shake off to hearing voices in the head urging murder. Mental illness can cause great distress not only to the sufferers, but to their families and friends. What makes life even harder for the sufferer is the stigma attached to such troubles, even in the 21st century.

A society which would shut out the great Churchill (and his black dog) is an impoverished one. We need a revolution in terms of acceptance and understanding of mental illness. Strange bedfellows like Alastair Campbell, Kjell Magne Bondevik, Crown Princess Masako and Celtic coach Neil Lennon are role models for that new compassionate direction.