Clan member goes across British Isle (9)
I believe the answer is:
tribesman
'clan member' is the definition.
(I've seen this in another clue)
'goes across british isle' is the wordplay.
'goes' becomes 'tries'.
'across' is an insertion indicator.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'isle' becomes 'man' (the Isle of Man is an example).
'tries' enclosing 'b' is 'tribes'.
'tribes'+'man'='TRIBESMAN'
(Other definitions for tribesman that I've seen before include "Society member" , "member of primitive group" , "Native" , "Family member" , "Primitive person'" .)