Support feature of a happy Londoner (5)
I believe the answer is:
pylon
'support' is the definition.
(I know that pylon is a type of pier)
'feature of a happy londoner' is the wordplay.
'feature of' says the answer is hidden in the clue.
'PYLON' is hidden within 'happy londoner'.
(Other definitions for pylon that I've seen before include "Tall cable carrier" , "Cable-holding frame" , "Electric cable tower" , "It marks turning point in a race" , "Electricity cable support" .)