We all have a dark side. The picture we show the world may include the cruel as well as the kind, or we may mask the uglier truth and contrive a display of innocence; but, acknowledged or hidden, Mr Nasty and Mr Nice are both actors in our play.

Unless, of course, it is possible to externalise: to contract out the necessary dirty work to a friend, keeping one’s own hands clean. Happy, then, the man who finds someone who (in the words of my former sketchwriting colleague Simon Hoggart) can do his hating for him. Tony Blair has found such a man.

And wretched the fellow who must do the hating. Alastair Campbell has played that part. Campbell is victim, not villain. The Project Inc has outsourced evil, making one unfortunate man the repository of its poisons, and soon that man must slink away into the wilderness, carrying away with him sins which were never committed for his own advantage but always on behalf of another who knew what had to be done and hired him to do it. Campbell has been the blank slate on which the Prime Minister’s dark side was written.

Many years ago I was by chance the witness to an early rehearsal of this strange role-playing. It is a story I have told already in The Times when extracts from my autobiography were serialised here last year. The way Campbell reacted to that serialisation became a story in itself. Both episodes are worth repeating for the light they shed now that he nears the end of his career at Downing Street.

Then it was just beginning. In 1994 I had shared with Alastair a BBC car to the Corporation’s Westminster studios where he and I formed (with Justin Webb) a three-man panel to interview each of the three contenders for the leadership of the Labour Party: Margaret Beckett, John Prescott, and (on this occasion) Tony Blair. At the same time as interviewing for the BBC and being assistant editor of the Today newspaper, Campbell was in fact working with Blair’s election team, but I did not know this.

Between mobile phone calls to somebody about the impending interview, he had asked me what questions I planned to put to Mr Blair, then talked me out of asking about the London Oratory, the school where the Blairs were planning to send their son Euan. Alastair persuaded me as a fellow journalist that this was irrelevant and I would look cheap to raise it; so I scrapped the question. If I had known Campbell was already working with Blair’s campaign I would have discounted his advice, for Euan’s schooling was to become a huge story.

I was the weakest interviewer. Campbell was fairly brutal with Prescott and Beckett but at least as unsparing with Blair himself. He seemed able to throw some kind of a switch and attack his future master; and his future master seemed unfazed. In review it resembles a role-playing game: Mutt versus Jeff, hard cop, soft cop.

I am not suggesting the performance was rehearsed, but that each man was already learning to slip into contrasting roles, so that the jumbled greys of their political world clarified into a darkness and a light: two men, two phials. Here, in elegant vignette, Tony Blair was attacking himself — by proxy.

When last autumn The Times’s pre-publication serialisation of my book included this story, there was an error in my text. I said Euan was at the London Oratory. He had not been. Campbell spotted this. The Times and my publishers, Penguin, were bombarded with faxes from him on 10 Downing Street headed notepaper, pointing out that Euan had joined the school nearly a year later.

So my story, said Campbell, must be a fiction. He added that he had no recollection of sharing a car with me. He said my whole reliability as a witness was now in question, casting doubt on the rest of my book. He wanted The Times to publish his letter and demanded that Penguin alter my book (already printed) or he would take advice on blocking its distribution.

Campbell did not mention that shortly before our interview with Blair, the Daily Express had trumpeted the Blairs’ plans to send their son to the Oratory. The tense I had used was certainly wrong, but beside the point. I had been careless and culpably so, but the burden of my report had been honest and right.

To my inexpressible relief I found the Daily Express article in the archives. Later I found the BBC tapes of our interviews. Penguin was able to ignore Campbell’s correspondence. Until then I had been wondering whether I had imagined the whole episode. For a miserable few days I had begun to doubt my own rationality. I feel for Andrew Gilligan now.

Are you not struck by the parallel with the song-and-dance Campbell has now organised about whether he personally inserted the 45-minute warning, and whether the late Dr David Kelly was — as the BBC suggested — a senior “intelligence” source? That probably was the wrong phrase — but you may share my reaction that Dr Kelly was rather more important than a senior intelligence source. “Intelligence” covers a multitude of sinners. I have worked with some of these (in 1974 they offered me a full-time job in MI6) and can assure you that they include all sorts and can offer all sorts of opinions.

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