Invaluable American fuel English brought to the front (6)
I believe the answer is:
useful
'invaluable' is the definition.
(something useful is valuable)
'american fuel english brought to the front' is the wordplay.
I cannot really understand how this works, but
'american' could be 'us' (abbreviation for United States) and 'us' is found within the answer.
an anagram of 'fuel' is 'eful' which is located in the answer.
No letters remain.
This explanation may well be incorrect...
(Other definitions for useful that I've seen before include "Of service" , "Effective" , "Utilitarian" , "Beneficial" , "Handy, practical" .)