House workers’ representatives before party by river (5)
I believe the answer is:
tudor
'house' is the definition.
(royal house)
'workers' representatives before party by river' is the wordplay.
'workers' representatives' becomes 'TU' (abbreviation for trade union).
'before' means one lot of letters go next to another.
'party' becomes 'do' (do is a kind of party).
'by' is a charade indicator (letters next to each other).
'river' becomes 'r' (abbreviation for river).
'tu'+'do'+'r'='TUDOR'
(Other definitions for tudor that I've seen before include "Mary" , "Member of the dynasty ruling England 1485-1603" , "Member of royal family" , "A royal house of England" , "Elizabeth I of England was of this royal family" .)