‘I love to lose myself in a mystery’, Sir Thomas Browne confesses in Religio Medici. I know what he means. There are few more enjoyable pastimes than snuggling up with a good murder. But such mysteries are penetrable, ‘susceptible of rational explanation’ as Sherlock Holmes might say. Holmes, incidentally, is currently to be seen in a marvellous new incarnation on ITV every week, played by Jeremy Brett, who has overcome the fact that as a young man he was, to use a phrase of Anthony Burgess’s, ‘irrelevantly endowed with adventitious photogeneity’ and is now, in his maturity, acting magnificently. In the current series we have been treated to ‘The Copper Beeches’ and ‘The Greek Interpreter’, in both of which ‘all of my friend’s remarkable powers were needed’.

But I know of a problem, a twentieth century mystery, which would appear to be beyond all hope of unravelling, and which would surely have taxed the Masters themselves. The question is this: what is the name of the substance that sloshes about inside the heads of television programme controllers