Defiant trade union is out around Britain (13)
I believe the answer is:
insubordinate
'defiant' is the definition.
('insubordinate' can be similar in meaning to 'defiant')
'trade union is out around britain' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'around' indicates putting letters inside.
'britain' becomes 'b' (common abbreviation as in GB).
'trade'+'union'+'is'='tradeunionis'
'tradeunionis' with letters rearranged gives 'insuordinate'.
'insuordinate' going around 'b' is 'INSUBORDINATE'.
(Other definitions for insubordinate that I've seen before include "Insolent" , "challenging authority" , "Mutinous" , "Badly behaved" , "Rebellious" .)