What are (themed) cryptic crossnumber puzzles and where do they appear?

I'll start by answering the second question first, as that is the easier. This rather unusual genre of puzzle appears quarterly as part of the series of Listener crosswords, which found a new home in The Times newspaper following the demise of The Listener magazine in 1991. There is also a monthly on-line crossword magazine called The Magpie, which has a numerical puzzle in each issue. As a result, fans of crossnumber puzzles have sixteen a year to tackle. Themed cryptic crosswords appear much more frequently – perhaps ten times as often.

All Listener puzzles have a title and the setter is given a pseudonym. They are also numbered, and in what follows this reference is given in square brackets following the letter L. Puzzles from the The Magpie are referenced according to the issue of the magazine, using M.