Trader in railway location, one down the line from Victoria (9)
I believe the answer is:
stationer
'trader' is the definition.
(I know that stationer is a type of merchant)
'railway location one down the line from victoria' is the wordplay.
'railway location' becomes 'station'.
'one down the line from victoria' becomes 'ER' (Elizabeth Regina, descendant of Queen Victoria).
'station'+'er'='STATIONER'
'in' is the link.
(Other definitions for stationer that I've seen before include "Writing-materials shop" , "I supply rulers: for example" , "Tradesman" , "Seller of paper, pens, etc" , "Retailer of writing materials etc" .)