Attack occupying leading group, staying very much around island (8)
I believe the answer is:
invasion
'attack' is the definition.
(I know that invasion is a type of attack)
'occupying leading group staying very much around island' is the wordplay.
'occupying' becomes 'in' (I've seen this in other clues).
'leading group' becomes 'van' (I've seen this before).
'staying' is an insertion indicator (stay could historically mean to imprison).
'very much around island' becomes 'sio' (I can't justify this - if you can you should give a lot more credence to this answer).
'van' enclosing 'sio' is 'vasion'.
'in'+'vasion'='INVASION'
Can you help me to learn more?
(Other definitions for invasion that I've seen before include "Encroachment by enemy" , "Occupation" , "Unwelcome encroachment on another country" , "Unwelcome intrusion" , "Hostile incursion" .)