Out Briton in broadcast after Conservative donation (12)
I believe the answer is:
contribution
'donation' is the definition.
(synonyms)
'out briton in broadcast after conservative' is the wordplay.
'broadcast' indicates an anagram.
'after' means one lot of letters go next to another.
'conservative' becomes 'C' (abbreviation commonly used in UK politics).
'out'+'briton'+'in'='outbritonin'
'outbritonin' is an anagram of 'ontribution'.
'ontribution' after 'c' is 'CONTRIBUTION'.
(Other definitions for contribution that I've seen before include "given financial assistance" , "Gift" , "Something given towards a common purpose" , "Input" , "Something given towards a common aim" .)