Former partner strongly criticises European extension (7)
I believe the answer is:
expanse
'extension' is the definition.
(thesaurus)
'former partner strongly criticises european' is the wordplay.
'former partner' becomes 'ex'.
'strongly criticises' becomes 'pans'.
'european' becomes 'e' (abbreviation e.g. EU).
'ex'+'pans'+'e'='EXPANSE'
(Other definitions for expanse that I've seen before include "Swathe" , "reach" , "Wide area of open land or space" , "Range - spread" , "considerable area" .)