Furious, means to escape across English border (8)
I believe the answer is:
vehement
'furious' is the definition.
(thesaurus)
'to escape across english border' is the wordplay.
'to escape' becomes 'vent' (I've seen this in other clues).
'across' is an insertion indicator.
'english' becomes 'e' (abbreviation).
'border' becomes 'hem' (I've seen this before).
'e'+'hem'='ehem'
'vent' going around 'ehem' is 'VEHEMENT'.
'means' acts as a link.
(Other definitions for vehement that I've seen before include "Even them being intense, showing strong feeling" , "Forcefully emphatic" , "Vigorously emphatic" , "Forcible" , "Vigorous, emphatic" .)