Your passenger is very left-wing (6,9)
I believe the answer is:
fellow traveller
'your passenger' is the definition.
I can't judge whether this definition defines the answer.
'very left-wing' is the wordplay.
I cannot really understand how this works, but
'very' could be 'v' (abbreviation) and 'v' is present in the answer.
'left' could be 'l' (common abbreviation) and 'l' is located in the answer.
'wing' could be 'ell' (ell is a kind of wing) and 'ell' is located in the answer.
This explanation may well be incorrect...
'is' is the link.
Can you help me to learn more?
(Other definitions for fellow traveller that I've seen before include "one with leftist leanings" , "possibly 18 [PARTISAN]" , "left supporter" , "political ally" , "we meet on the 4.50 from Paddington?" .)