Secret coup I organised, being fixated on sovereignty (11)
I believe the answer is:
eurosceptic
'being fixated on sovereignty' is the definition.
(person sceptical of the EU)
'secret coup i organised' is the wordplay.
'organised' is an anagram indicator.
'secret'+'coup'+'i'='secretcoupi'
'secretcoupi' with letters rearranged gives 'EUROSCEPTIC'.
(Other definitions for eurosceptic that I've seen before include "One against being "ruled from Brussels"" , "hostile to union" , "type of politician" , "one not keen on Brussels" , "One opposed to closer links with our Continental neighbours" .)