It was early in the millennium that Sir David Attenborough conducted us through the “Blue Planet”, the BBC’s astonishing exploration of the world’s oceans and the life which they sustain. So enthralling did I find it that somehow I haven’t had the heart to watch its replacement, Blue Planet 2, although I’m told that it was just as good. Justification, you might think, for a State broadcaster lavishly funded by a special tax? Or perhaps…