Gold, British crown jewel (3)
I believe the answer is:
orb
'crown jewel' is the definition.
'orb' can be an answer for 'crown' (thesaurus). I'm not certain of the 'jewel' bit.
'gold british' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'british' becomes 'b' (abbreviation e.g. in BBC).
'or'+'b'='ORB'
Can you help me to learn more?
(Other definitions for orb that I've seen before include "Item of royal regalia" , "A sphere or globe" , "Part of royal regalia" , "ball with cross" , "Item of insignia" .)