Effect of insidious banks taking legal action (5)
I believe the answer is:
issue
'effect' is the definition.
(I know that effect can be written as issue)
'insidious banks taking legal action' is the wordplay.
'banks' means to remove the middle letters (the sides or banks of the word).
'taking' says to put letters next to each other.
'legal action' becomes 'sue' (as in suing in court).
'insidious' with its middle removed is 'is'.
'is'+'sue'='ISSUE'
'of' acts as a link.
(Other definitions for issue that I've seen before include "Offspring; problem" , "Subject of debate" , "Come forth or bring out" , "Emit" , "Topic; send out" .)