Send up one British fellow to US agency (3)
I believe the answer is:
fbi
'us agency' is the definition.
'FBI' can be an answer for 'agency' (FBI is an example). I'm not certain of the 'us' bit.
'send up one british fellow' is the wordplay.
'send up' says the letters should be written backwards.
'one' becomes 'i' (Roman numeral).
'british' becomes 'b' (abbreviation e.g. in BBC).
'fellow' becomes 'F' (abbreviation - of a society etc.).
'i'+'b'+'f'='ibf'
'ibf' written backwards gives 'FBI'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for fbi that I've seen before include "J. Edgar Hoover long its director" , "J. Edgar Hoover's organisation" , "law enforcers" , "Initially, J Edgar Hoover's law force" , "US law enforcement agency" .)