Of all the ingredients in whose absence no BBC radio programme seems able to proceed these days – the honeyed tones of Ms Mariella Frostrup, the doleful sarcasm of Will Self, endless MacGregorian part-works – by far the most vital seems to be a live audience. No Radio 4 comedian can open his mouth without a continuous shrieking from the middle distance, and the recent production of A Christmas Carol was effectively broadcast pantomime. If you can sympathise with the purist who deplores these tendencies, on the grounds that radio is a compact between voice and listener, then you can also allow that there are times when a live audience is worth its wages, or rather its free ticket, and one of them was Matthew Sweet’s look at the popular culture of the Great War.In fact, th