The most common and most likely answer to this crossword clue is the 3 plus 6 letter word YES PLEASE
I've seen this crossword clue in The Guardian
Y
E
S
P
L
E
A
S
E
Buddy explains!
The straight part
We know that "You get no thanks opposing such/willing consent" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case you get no thanks opposing such/willing consent = yes please.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.