Economy? British Minister heading off financial centre (7)
I believe the answer is:
brevity
'economy?' is the definition.
(thesaurus)
'british minister heading off financial centre' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'minister' becomes 'rev' (I've seen this before).
'heading off' means to remove the first letter.
'financial centre' becomes 'city'.
'city' with its first letter removed is 'ity'.
'b'+'rev'+'ity'='BREVITY'
(Other definitions for brevity that I've seen before include "The soul of wit?" , "Concision" , "Conciseness" , "considered the essence of wit" , "Terseness" .)