Performance going ahead in London district (5)
I believe the answer is:
acton
'london district' is the definition.
(I've seen this before)
'performance going ahead' is the wordplay.
'performance' becomes 'act' (act is a kind of performance).
'going' becomes 'on' (both can mean functioning or activated).
'ahead' is a charade indicator (letters next to each other).
'act'+'on'='ACTON'
'in' acts as a link.
(Other definitions for acton that I've seen before include "Gladstone's adviser" , "English statesman" , "somewhere in London" , "London area" , "District of West London" .)