17a Wanting more, slice of gâteau with extra piping (8) - - - e - - - r
23a Pair of kings? You could do better (3-3) - - - t - -
12d President of Spain in canyon with scrubland (6,4) -e - - - e - - - h
16d No-good silver-tongued weaselly type written up in book (8) - - - r - - - o