Every so often the Radio 4 schedules throw up a work of such startling obscurity that one pauses to wonder how exactly how it got past the commissioning editor. My all-time favourite in this line was a feature from some years ago in which the members of a tape-recording club in 1960s Derby reminisced about their activities. If not quite in this ­category, then this account of an imaginary luncheon enjoyed by the novelist Elizabeth Bowen and the poet John Betjeman at the Shelbourne Hotel, Dublin, in 1942 (14 February) ran it tantalisingly close.The resolutely recherché nature of the piece ran far beyond its assumption that the audience would have a working knowledge of frontman and -woman. No, for a real appreciation of what was going on, the listener needed to have heard of Isa