Phil, jono, adnarim, crosbie: re 12a, I parsed this thinking that if someone says that to you, it’s a good idea to scarper - quickly! But maybe it makes more sense thinking of dyes, or held firm perhaps. I do like my parsing though, mainly cos it made me laugh.
ParadigmShifter, 19d was my LOI too. I got it from the cryptic part but needed google to confirm that it’s a word.
Pretty straightforward puzzle, but enjoyable all the same.