Reader worried by European voters (10)
I believe the answer is:
electorate
'voters' is the definition.
(I've seen this in another clue)
'reader worried by european' is the wordplay.
'reader' becomes 'lector' (synonyms).
'worried' becomes 'ate' (something worrying may eat someone up).
'by' is a charade indicator (letters next to each other).
'european' becomes 'E' (abbreviation e.g. EU).
'lector'+'ate'='lectorate'
'lectorate' after 'e' is 'ELECTORATE'.
(Other definitions for electorate that I've seen before include "Everyone choosing" , "Those qualified to vote" , "Voters as a whole" , "Voters collectively" , "Voters in general" .)