Defiant criminal undoes Britain (13)
I believe the answer is:
insubordinate
'defiant' is the definition.
('insubordinate' can be similar in meaning to 'defiant')
'criminal undoes britain' is the wordplay.
'criminal' indicates anagramming the letters.
'undoes'+'britain'='undoesbritain'
'undoesbritain' with letters rearranged gives 'INSUBORDINATE'.
(Other definitions for insubordinate that I've seen before include "undisciplined" , "Badly behaved" , "Defiant of authority" , "Not submissive to authority" , "Mutinous" .)