Charles Kennedy was a victim of one of the most remarkable shifts in political alignment in British history

Here was the ruthless spin-doctor who was accused of sexing up the so-called "dodgy dossier" (which made the Blair government's case for war in Iraq) - and led the assault on the BBC after one of its journalists made the accusation.

Charles Kennedy opposed the Iraq war in 2003, at great personal cost, and challenged the nonsense about British citizens being only 45 minutes away from an attack by Saddam Hussein's non-existent weapons of mass destruction.

But Kennedy and Alastair Campbell were apparently great friends. Friendship often crosses the political divide, as the SNP's new MPs are going to find out. The Tories may be the hated enemy, but after a while in Westminster the conviviality gets to you.They'll discover that Conservative politicians can often be very nice people, and not the heartless toffs of party propaganda.

Also, that their political opponents often aren't the problem. As the old Commons saying goes: forget the opposition, your real enemies are right behind you. Very often politicians find that they fall out bitterly with rivals on their own side of the gangway and quite enjoy a consoling glass with MPs from other parties.

There is also a long tradition of parliamentary celebration of your political opponents, as we saw last week with the generous tributes extended to Charles Kennedy, often from his greatest political rivals. The tributes are sincere, but everyone knows what the people making them said about the politicians behind their backs.

When someone truly exceptional like Charles Kennedy dies, everyone tries to get up close in the hope that some of his integrity rubs off on them. So I'm not going to indulge in the same tributes here. I knew Charles Kennedy well of course since he became and MP in 2003. And after he left politics I had further dealings with him when he was rector of Glasgow University and I was rector of Edinburgh.

But I would never pretend that I was his close personal friend. I sometimes wonder if friendship is really possible in politics because there is always so much going on beneath the surface. Certainly friendship between politicians and journalists is extremely difficult, and often undesirable.

Journalists seek to befriend politicians for often very dubious motives. Politicians may think they are talking to a friend when they are really talking to a ruthless professional who'd sell their soul for a front-page lead. And it's a two-way street. Politicians often befriend journalists in the hope of getting favourable treatment, a kind word, a bit of understanding in their coverage.

When I've said and written things I regret it has usually been because I was too close to the people involved. As a commentator, you have to be critical, and there has to be a professional distance. Which is regrettable and even makes working relationships seem a little cold. But public life is a bit like that. If you want a friend, get a dog.

So, what interests me about Charles Kennedy - rather than trying to pretend he was my great buddy - is how a politician like him can lose the plot so disastrously. He was the Liberal Democrats' most successful leader for 80 years, who won 62 seats in 2005, yet to many people he was "chat show Charlie", a bibulous lightweight and an embarrassment to his party.

Everyone went on last week about his alcoholism - sometimes referred to has his "demons". I could name a hundred politicians who drank. Winston Churchill started the day with a whisky, drank a bottle of Pol Roger champagne for lunch, and then began serious drinking in the evening. He seemed to manage it well enough to become Britain's greatest war leader.

A different age, you say - and of course it was. But I can't help wondering if we aren't missing something here. We expect our politicians to be sober men and women who don't have dark sides and never do anything at all in case it looks bad. Then we wonder why they're just empty suits.

I'm not sure the reputation was entirely justified. I can honestly say that in all the years I knew him I never once saw Charles Kennedy the worse for drink. But the post-mortem on his death at 55 was unequivocal: Charles Kennedy died of a massive haemorrhage caused by alcohol.

Alastair Campbell was on the air within minutes, calling for Westminster to take the lead in addressing our drink culture. He even commended the SNP Government in Scotland for taking the kind of action that Westminster has fudged.

The Scottish Government is pressing ahead with its attempt to set a minimum unit price for alcohol, which is being challenged by the Scotch Whisky Association in the European Court of Justice. I wonder how they're feeling this weekend?

The First Minister, Nicola Sturgeon, received some unwanted support from Conservative Eurosceptics after her speech last week in Brussels when she called for Scotland to be free to set its own limits and laws on alcohol pricing. Actually, there is good evidence that Scotland's drink culture is on the decline. Scots have been drinking less in recent years and alcohol-related deaths have fallen by 35% since 2003.

But even though pubs are closing by the thousand - partly through some of the most draconian drink driving penalties in Europe - Scots still have a drinking problem. We drink more than the rest of the UK and admissions for alcohol-related problems are higher here.

Though of course, the very worst place for anyone with a drink problem is the Palace of Westminster. I once went on a pub crawl there on behalf of a newspaper and lost count after 15 bars. Some of these have since closed, I gather. But the place is still saturated in booze.

Yet when it comes down to it, I don't actually think that it was his drinking that led to Charles Kennedy's defeat in last month's election. His constituents saw him in the close community around Fort William and knew all about his troubles - which, after all, weren't so different from their own.

People have suggested that the voters indeed let him down and may even have brought about his post-election depression. I don't believe that. They felt just the same about him after the election as before it, as the tributes from his voters demonstrated.

Rather, Charles Kennedy was a victim of one of the most remarkable shifts in political alignment in British history, a tsunami that swept away the old political order. The Liberal Democrats were wiped of the Scottish mainland along with Labour and the remnants of the Conservative Party.

The Liberals had represented the north of Scotland, and parts of the rural Borders, for over a century. We are in a very new Scotland following the events of 2014/15. It's a pity that Charles Kennedy won't be a part of it. He was the best in politics, as well as the worst.