Independent on Sunday 875 by Quixote Tricky in places

Some tricky clues – solving time 22 mins.    Hope setters are not paid by clue, just 24 in the puzzle.

ACROSS
5  GRIN AND BEAR IT  anagram of “Britain – danger” with the indicator “making characters jumpy”.  Very good surface, relating to topical issues, I guess.
10  ARGENT  Hair regularly thinned out = take every second letter i.e. ar + gent = bloke
12  DISOWN   Sown = broadcast “Introduced by” Di = woman.    Might have been princess pre-August 1997
14  SNAKED  S = little son i.e. abbreviation for son + naked.   Amusing surface.
19  SINGLE  Definition is “One”.   sin + gle(e)  endless merriment
20  ZENITH  Definition is “high point”  Zen + it + h (abbrev for hard)
21  MEASURES  Elaborate wordplay here.   The join between wordplay and definition is between “certain \ amounts” So it’s Quixote = me (the setter) + certain = sure in “starts to act silly” i.e in a s, the first letters of those two words.

DOWN
1 FITCHEWS   This is a new word for me and slowed me up a lot.  Fit = suitable  chews = things to get one’s teeth into.   That’s good.
2 CAVORT   v = very + o = old in cart.   Nice use of two meanings of lark as it’s the bird I’d pictured first.
3 BEAR DOWN   Tip for new solvers (feathers = down is very common in clues for phrases containing down)
13 WORTHIES  My favourite clue and the last I solved.   Anagram of “Who tries” -indicator “to sort out”.  I was trying to make an anagram of “great” and “the” at one stage.
15 KENTUCKY  Kent replacing l in lucky.  happy = lucky “to let learner leave for English county”
17 TRIAGE  “Little good” = g in anagram of “irate”