One night I let off last of explosive, being compliant (6,3,4)

I believe the answer is:

toeing the line

'being compliant' is the definition.
(toeing the line is a kind of being compliant)

'one night i let off last of explosive' is the wordplay.
'off' indicates an anagram.
'last of' says to take the final letters.
The final letter of 'explosive' is 'e'.
'one'+'night'+'i'+'let'='onenightilet'
'onenightilet' with letters rearranged gives 'toeingthelin'.
'toeingthelin'+'e'='TOEING THE LINE'

I've seen this clue in The Telegraph.

Want a hint initially instead of a full solution? Install my app