“ALEXAMENOS worships his God”, the scratchings proclaim under a picture of a soldier saluting a crucified figure who has the head of a donkey. It was found on a wall near the Palatine Hill in Rome, and is estimated to have been carved AD c.200. This early attack on Christianity was shown in the collage that opened A Brief History of Graffiti (BBC4, Wednesday of last week), whetting my appetite for some serious analysis of this age-old phenomenon. Alas — it was never referred to again.

We did get a few references to contemporary religious sloganising, but otherwise this aspect of the social menace was ignored. Dr Richard Clay’s conviction is that it is not a social menace at all, but that the defacing of blank walls expresses political dissent, repressed personal expression, or just sheer artistic ability, and that we should be grateful to those who mess up the sides of trains.

He drew on a ludicrously wide range of examples: in what sense are prehistoric cave-paintings graffiti? The mysterious Stone Age stencils of human hands might, as he said, be ways of making your mark, of saying “I was here”; but are they not more likely to have had some now impenetrable vital cultic purpose? Posters are not graffiti, and the New York spray-paint artists nowadays paid vast sums for their work can hardly be claimed to be producing graffiti.

The point about graffiti, I think, is that it is something you are not supposed to do, marking a surface that does not belong to you. Some examples are, of course, significant, revealing, or beautiful, and deserve serious attention — but they were not on offer here.

When Lucy Met Roy: Sir Roy Strong at 80 (BBC4, Sunday before last) was a retrospective studio interview of Hereford Cathedral’s most famous server — although, sadly, this aspect of his life was not referred to. Lucy Worsley is herself a quasi-ironic stylist in Sir Roy’s mould; so the couple were to some extent matched.

The serious issue that they rather fluttered around was how far all the things that Sir Roy most deprecates about museums today — their populism, commercialisation, and focus on blockbuster exhibitions — were all a wholehearted taking-up of exactly the radical innovations that brought such notoriety to his career.

But the ’60s archive film of him at the National Portrait Gallery and the V&A is quite astonishing. How did the Establishment of the day, supposedly so hidebound and reactionary, ever let him get away with it?

I have long fought against it, but must now concede: paradise does exist, and can be entered any weekday on CBeebies. In The Night Garden offers all the balm that any weary soul might need, aimed at very young children and reanimating the infant in all of us. The primary colours, simple songs, endless repetition of words and music, and constant hugging and kissing each time a basic task is completed speak deeply to our wounded psyche, and reveal the inspiration for the Alpha course and most Charismatic worship.

But enough cheap gags: I am completely won over by this glorious exposition of that most underrated Christian virtue: innocent delight.