Point of concert being performed by Conservative (10)
I believe the answer is:
'point' is the definition.
(I've seen this before)
'concert being performed by conservative' is the wordplay.
'concert' becomes 'prom' (abbreviation for promenade concert).
'being performed' becomes 'on' (eg a play may be 'on' at a particular theatre).
'by' is a charade indicator (letters next to each other).
'conservative' becomes 'tory' (informal term for a Conservative Party member).
'of' is the link.
(Other definitions for promontory that I've seen before include "Bluff" , "Coastal feature" , "Headland" , "Point" , "Bill" .)