See posh car shunting into railway truck (5)
I believe the answer is:
lorry
'railway truck' is the definition.
'lorry' can be an answer for 'truck' (lorry is a kind of truck). I'm not certain of the 'railway' bit.
'see posh car shunting' is the wordplay.
'see' becomes 'lo' (archaic exclamation meaning 'look!').
'posh car' becomes 'rr' (short for Rolls Royce).
'shunting' becomes 'y' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'lo'+'rr'+'y'='LORRY'
'into' is the link.
Can you help me to learn more?
(Other definitions for lorry that I've seen before include "HGV" , "Industrial vehicle" , "Large truck" , "Large motor vehicle for transporting goods" , "Commercial vehicle" .)