Different standard adopted by parliamentary constituency on energy (8)
I believe the answer is:
separate
'different' is the definition.
(thesaurus)
'standard adopted by parliamentary constituency on energy' is the wordplay.
'standard' becomes 'par' (standard of play in golf).
'adopted by' indicates putting letters inside (I've seen this in other clues).
'parliamentary constituency' becomes 'seat' (as in a seat in parliament).
'on' means one lot of letters go next to another.
'energy' becomes 'e' (physics symbol as in E=mc2).
'par' inserted within 'seat' is 'separat'.
'separat'+'e'='SEPARATE'
(Other definitions for separate that I've seen before include "Distinct, not joined" , "Divided -- distinct" , "Dinstinct or discrete" , "Divided or detached" , "Divide, keep apart" .)