Following intelligence, top spy infiltrates gathering on the quiet (10)
I believe the answer is:
informally
'following intelligence top spy infiltrates gathering on the quiet' is the definition.
I can't tell whether this defines the answer.
'intelligence top spy infiltrates gathering on the quiet' is the wordplay.
I cannot quite understand how this works, but
'intelligence' could be 'info' (I've seen this before) and 'info' is located in the answer.
'spy' could be 'm' ('M' is James Bond's boss) and 'm' is present in the answer.
'gathering' could be 'rally' (rally is a kind of gathering) and 'rally' is present in the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for informally that I've seen before include "off the record" , "in relaxed fashion" , "in relaxed manner" .)