Here M40 leads Oxford type, say, learner ahead to West (6)
I believe the answer is:
london
'here m40 leads oxford type' is the definition.
The answer is a location as well as being a singular noun. This is suggested by the definition.
'learner ahead to west' is the wordplay.
'learner' becomes 'l'.
'ahead' becomes 'on' ('on' can be a synonym of 'ahead').
'to west' becomes 'don' (I can't explain this - if you can you should believe this answer much more).
'l'+'on'+'don'='LONDON'
'say' acts as a link.
Can you help me to learn more?
(Other definitions for london that I've seen before include "City for the non-old, oddly" , "England's capital city" , "Where Boris Johnson might be" , "- Clay; - pride; - plane" , "Jack - , US author (White Fang); city" .)