Fashioning a tin brain as a national symbol (9)
I believe the answer is:
britannia
'a national symbol' is the definition.
(I know that Britannia is a national symbol)
'fashioning a tin brain' is the wordplay.
'fashioning' is an anagram indicator.
'a'+'tin'+'brain'='atinbrain'
'atinbrain' is an anagram of 'BRITANNIA'.
'as' acts as a link.
(Other definitions for britannia that I've seen before include "our sitting representative" , "National representative" , "She who musically rules the waves" , "province" , "Female warrior" .)