Unwelcome intrusion (8)
I believe the answer is:
invasion
'unwelcome intrusion' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for invasion that I've seen before include "Occupation" , "Encroachment by an army" , "Unwelcome encroachment on another country" , "Hostile incursion" , "Unwelcome intrusion" .)