Is this writer fired up about British capital? (7)
I believe the answer is:
tbilisi
'capital?' is the definition.
(capital of georgia)
'is this writer fired up about british' is the wordplay.
'this writer' becomes 'I' (the person who is writing these clues).
'fired' becomes 'lit' (set on fire).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'about' is an insertion indicator.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'is'+'i'+'lit'='isilit'
'isilit' backwards is 'tilisi'.
'tilisi' placed around 'b' is 'TBILISI'.
(Other definitions for tbilisi that I've seen before include "Georgian capital" , "Georgian city" , "Georgian place" , "Capital city of Georgia" .)