Great Britain, poor, banking two pounds (9)
I believe the answer is:
brilliant
'great' is the definition.
(I know that great can be written as brilliant)
'britain poor banking two pounds' is the wordplay.
'poor' is an anagram indicator.
'banking' is an insertion indicator.
'two' indicates the doubling of some letters.
'pounds' becomes 'L' (abbreviation e.g. Lsd - pounds, shillings, pence).
'britain' is an anagram of 'briiant'.
'l' doubled is 'll'.
'briiant' going around 'll' is 'BRILLIANT'.
(Other definitions for brilliant that I've seen before include "Glittering" , "Fantastic!" , "Magnificent" , "Shining intensly" , "Very bright or vivid" .)