Criminal in France, very old-fashioned royal (10)
I believe the answer is:
trespasser
'criminal' is the definition.
(someone trespassing someone else's property)
'in france very old-fashioned royal' is the wordplay.
'in france very' becomes 'tres' ('very' in French).
'old-fashioned' becomes 'passe' (synonyms).
'royal' becomes 'r' (abbreviation).
'tres'+'passe'+'r'='TRESPASSER'
(Other definitions for trespasser that I've seen before include "Uninvited visitor" , "sinner" , "One unlawfully entering another's land" , "Intruder into another's land" , "Misplaced individual" .)