Dominic Lawson: The harsh truth: If you hold the highest offices of state, you will be driven mad

There is a sense of omnipotence which causes normal caution to be cast aside

It is one of the strange foibles affecting all humanity that we tend to see our own faults in others, whether they share them or not. In this respect, Alastair Campbell's revelations in last weekend's Independent on Sunday about his own fragile mental state explain something which I had not previously been able to understand.

When Mr Campbell was in charge of media relations at 10 Downing Street, he was given to describing errant Cabinet ministers as bonkers. It was an unusual technique and one that happened too often to be dismissed as mere coincidence.

The most celebrated example - although Campbell has never owned up to it publicly-is his description of Gordon Brown as having "psychological flaws". It was a clever phrase, as you would expect from Campbell: in a sense we all have psychological flaws, but it conveyed a quite different meaning in this case, which was that the Chancellor was a bit peculiar, and that this, rather than reason, explained much of Mr Brown's conduct towards Mr Blair.

When Ron Davies, the then Secretary of State for Wales, became the first of Mr Blair's Cabinet ministers to resign (following an unfortunate encounter with another man on Clapham Common), Mr Campbell, as was his wont, drafted not just the Prime Minister's letter accepting the resignation but also Ron Davies' public mea culpa. He obliged Mr Davies to sign a letter to say that he had suffered from "a moment of madness".

When, three years later, Peter Mandelson was forced out of office for the second time, largely at Mr Campbell's urging, the lobby correspondents reported that "Downing Street" - that is to say Mr Campbell himself - had said that Mr Mandelson had become "slightly detached". The correspondents asked the Prime Minister's spokesman whether he was questioning Mr Mandelson's "state of mind". Was it another "moment of madness"? "Yes, I think it was" said Mr Campbell. Naturally Mr Mandelson bitterly disputed the opinion that he had gone doolally, but it's the Catch- 22 of madness that its denial is usually taken as confirmation.

Last Sunday, Campbell rather courageously chose to mark something called World Mental Health Day by revealing his own mental history. He said that at the age of 28 he had been "depressed for a long time. You wake up and can't open your eyes. You can't find the energy to brush your teeth, the phone rings and you stare at it endlessly."

Previously, Campbell had been seen just as a man who had had troubles with drink, but this interview demonstrated that his alcohol dependency had been a symptom rather than a cause of his psychosis. More intriguingly, Campbell went on to say that "when I worked at Number 10 there were periods when I felt depressed."

Once, he said, he had felt "unable to face" giving a briefing. I am tempted to say that it was, rather, a moment of sanity in which Campbell felt unable, on one occasion, to explain to lobby correspondents how everything was going according to plan - that his rational mind must suddenly have reasserted itself, insisting that the "line to take" was too unbelievable even for a man of Mr Campbell's skills to defend.

I am puzzled, also, by Alastair Campbell's conflation of a genuine psychotic episode in his twenties - he realised he had to seek urgent medical attention when he found himself driving aimlessly round and round a roundabout - with what seems nothing more than the inevitable moments of extreme anxiety in situations of very high stress. As I understand it, clinical depression is not the sort of wretchedness which all of us have suffered from at one time or another - an occasionally irrational misery is inevitably part of the human condition - but a physically overwhelming force which renders the sufferer a zombie. In that context there is something slightly off-putting in Campbell's revelation that his lowest moment during his time at No 10 was when he heard that the weapons scientist Dr David Kelly had killed himself.

For it was Campbell who, short of actually naming Dr Kelly as the source for Andrew Gilligan's story that the Government had knowingly distorted the evidence that Saddam Hussein had weapons of mass destruction, did more than anyone to steer the press towards the identification of the Ministry of Defence scientist. As was clear from his widow's evidence to the Hutton Inquiry, it was the consequences of that public identification which drove Dr Kelly to kill himself.

It was manifest in Mrs Kelly's most affecting answers to Lord Hutton, that her husband had been suffering from clinical depression having become an unrecognisably isolated and withered personality. Unlike Campbell, Dr Kelly had become a completely powerless individual, just a victim of circumstance - the circumstance being the absolute impermissibility that the Prime Minister should be seen as having in any way manipulated the intelligence on which this country went to war in Iraq.

On the day after Mr Campbell's personal revelations, David Blunkett attempted a similar declaration with the first tranche of the serialisation of his diaries. He claimed, in Monday's installment, that during the furore over his public falling out with his former mistress, Kimberly Quinn, he had "thought that I was going mad".

It was the Sunday Telegraph, which I then edited, that broke the story of Mr Blunkett's personal connection to the Home Office's fast-tracking of a permanent residency visa for Mrs Quinn's Filipina nanny; I recall later receiving a letter from Mr Blunkett which indeed made me think that he was no longer as rational as one would hope for in the man who had been charged with our national security.

David Blunkett had in fact been suffering from the kind of madness which seems to affect a dangerously high proportion of people who attain positions of power - a sense of omnipotence which causes normal caution to be cast aside. In this case, Blunkett was, in the colloquial rather than clinical sense of the word, "mad", to think that he could get away without scrutiny of his conduct in an affair with the publisher of a Conservative current affairs magazine, who was herself married to a much-liked figure in the media. What Blunkett described as "mad" was in fact reality dawning upon him, as he became aware of how crazy he had been.

Perhaps it is the case that in the positions of greatest power a sort of madness is essential for survival - the madness that allows a leader to carry on in a straight line when everyone around him is frantically looking for the sign marked "exit". For a proper explanation of that psychological condition, however, we shall probably need to wait for the publication of the diaries of Tony Blair - or perhaps those of his part-time counsellor, a former psychiatric social worker called the Rt Hon Tessa Jowell.

d.lawson@independent.co.uk