Head of English in pursuit of more flashy underwear (9)
I believe the answer is:
brassiere
'underwear' is the definition.
'head of english in pursuit of more flashy' is the wordplay.
'head of' says to take the initial letters.
'in pursuit of' means one lot of letters go next to another.
'more flashy' becomes 'brassier' ('brassy' can be a synonym of 'flashy').
The initial letter of 'english' is 'e'.
'e' after 'brassier' is 'BRASSIERE'.
(Other definitions for brassiere that I've seen before include "garment" , "support" , "Female undergarment supporter" .)