Long to follow Peter's grand manner (7)
I believe the answer is:
panache
'grand manner' is the definition.
(I've seen this before)
'long to follow peter's' is the wordplay.
'long' becomes 'ache' ('ache' can be a synonym of 'long').
'to follow' is a charade indicator (letters next to each other).
'peter' becomes 'pan' (I've seen this in other clues).
'ache' after 'pan' is 'PANACHE'.
(Other definitions for panache that I've seen before include "Flamboyant sense of style" , "Swagger, grand manner" , "flourish" , "Sense of style, swagger" , "'Dash, flair (7)'" .)