Some presenters and producers are happy with such unpredictability. The late Roy Porter’s programmes were all the better for his apparent lack of planned control. A busy man, he used to turn up having done very little preparation, beyond ensuring an interesting spread of guests. He would trust those guests to have interesting things to say and then let the programme happen. The result could be brilliant as well as fascinatingly erratic. Porter was quite capable of turning up at the studio late, having phoned in to cajole his anxious producer into writing the introductory script. As listeners quickly understood, however, he had also spent his entire life as a historian ‘preparing’ for his programmes.

Other presenters, who lack such assurance, go in with a list of prearranged questions and then stick to them come what may. The result is often infuriating. An illusion of presenterly control is maintained, but at the expense of the conversation, which is constantly being bossed into line and redirected away from its own discoveries. Unpredicted turns in the conversation don’t stand a chance with presenters of this ilk. The producer may be comforted to feel that at least he knows where he is and can stay in control of timings as the recording goes ahead. Not so the ‘guests’, who are likely to come out of the studio feeling that they have just been dragged through a dense and spiky thicket to no purpose at all. Listeners, I suspect, are often inclined to agree.