Flash car saving energy as well (8)
I believe the answer is:
moreover
'as well' is the definition.
(thesaurus)
'flash car saving energy' is the wordplay.
'flash' becomes 'mo' (I've seen this in other clues).
'car' becomes 'rover' (former British car manufacturer**).
'saving' means one lot of letters goes inside another.
'energy' becomes 'e' (physics symbol as in E=mco).
'rover' placed around 'e' is 'reover'.
'mo'+'reover'='MOREOVER'
(Other definitions for moreover that I've seen before include "Furthermore, in addition" , "as well" , "Besides, in addition" .)