Highest office causes division (11)
I believe the answer is:
premiership
'highest office' is the definition.
'premiership' can be an answer for 'office' (premiership is a kind of office). I am unsure of the 'highest' bit.
'causes division' is the wordplay.
I cannot really understand how this works, but
'causes' could be 'premiers' (premier is a kind of cause) and 'premiers' is present in the answer.
The remaining letters 'hip' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for premiership that I've seen before include "the PM's office" , "Liverpool's office" , "Victory in competition" , "main football clubs" , "Office of Prime Minister" .)