Some years ago, an old friend, a building engineer by profession, pressed upon me a home-made CD-ROM and urged me, as a journalist, to do something with it. It was, he explained, full of documents proving that the Twin Towers were brought down by controlled explosions and not by the impact of a couple of airliners full of aviation fuel.

I put the disc in my filing cabinet and never mentioned it again. I did not think pursuing it would do any good to either of our reputations. Conspiracy theories – even coming from apparently sane, trustworthy people – have always left me cold.

Consequently, I was unimpressed with the early part of 9/11: Truth, Lies and Conspiracies (13 September). It introduced a couple of representatives of the “truther” movement, who have pulled together a number of puzzling anomalies in the official account of the terrorist attacks and used them to argue that there were no attacks at all: instead the towers had been brought down by the United States Government as a pretext for war. The television images we all saw were clever computer graphics.