Fed up with English court inadequacy (6)
I believe the answer is:
defect
'inadequacy' is the definition.
(thesaurus)
'fed up with english court' is the wordplay.
'fed up' becomes 'def' ('fed' going up in a down clue).
'with' says to put letters next to each other.
'english' becomes 'e' (abbreviation).
'court' becomes 'ct'.
'def'+'e'+'ct'='DEFECT'
(Other definitions for defect that I've seen before include "Flaw; turn traitor" , "mistake" , "Abandon one's country in favour of an opposing one" , "Fault - default" , "go over to the other side" .)