The answer to 18 down is ‘lipogram’, which means a piece of writing from which all words containing a particular letter have been deliberately omitted. The puzzle (and the clues as well, which is why their phrasing may seem a bit odd) is itself a lipogram, omitting the most common letter in English: E.
All the other letters of the alphabet DO appear in the grid. Since puzzles using the whole alphabet are known as pangrammatic, maybe this one is “pen-pangrammatic”?
Solvers may or may not care also to spot that this puzzle has a “Radio Times”-style grid in which each number represents only an across or down clue (not both) so that a single list of clues is sufficient.
