My public caricature - that of a self-confident alpha male - is only partly accurate.

In an ideal world, it would not take a film star to get the media focused on mental illness.

For all that the papers would say I was a liar, I took the words I was saying at briefings as seriously as Tony Blair took what he would say at the Despatch Box. I find it very difficult not to tell the truth. I felt I was accountable for what I said.

Friends have suggested that I am the least qualified person to talk about happiness, because I am often down, and sometimes profoundly depressed. But I think that's where my qualification comes from. Because to know happiness, it helps to know unhappiness.

My closest friend, who died not long ago, is buried near Marx's grave in Highgate cemetery, so I see the gaggle of admirers laying roses at the foot of his tombstone regularly. I have never been tempted to leave flowers there myself. Great theories, shame about the practice. Marx did many things. But inventing class was not one of them.

I have always been driven. I have always believed in what I believe very deeply.

I remember talking to Alex Ferguson about Tony [Blair] and Gordon [Brown], and he said: "Why doesn't Tony just get rid of him?" But if you sack someone in football, they can't turn up to training the next day. In politics they're still on the pitch. Gordon would still have been a big player.