Britain undoes changes being ungovernable (13)
I believe the answer is:
insubordinate
'ungovernable' is the definition.
(thesaurus)
'britain undoes changes' is the wordplay.
'changes' is an anagram indicator.
'britain'+'undoes'='britainundoes'
'britainundoes' anagrammed gives 'INSUBORDINATE'.
'being' acts as a link.
(Other definitions for insubordinate that I've seen before include "Rebellious" , "Mutinous" , "Recalcitrant" , "Insolent" , "challenging authority" .)