Supporter of the Reds on the same train as me? (6,9)
I believe the answer is:
fellow traveller
'supporter of the reds' is the definition.
(person sympathetic to communism)
I don't understand the rest of the clue.
(Other definitions for fellow traveller that I've seen before include "Like monk for nun in Chaucer, for example" , "like gypsy" , "left supporter" , "political ally" , "possibly 18 [PARTISAN]" .)