I really enjoyed 25a. 😃 Not come across this use of “parameters” before, but I have just dabbled in cryptic crosswords over the years and only recently have been participating regularly, so maybe it’s well known? Smit I was also looking for a Clue reference for ages - I became a fan as a teenager and have loved the long-running Radio 4 gem ever since (now in my 50s). Oh how Tim Brooke-Taylor will be missed.
19a thanks for the explanation Brendan. A new word to add to my lexicon! It was obvious what the answer was, but not why.
I have been using the Guardian Puzzles app (since lockdown started in March) and would be interested to hear how others access the Guardian crosswords.