Expert in middle of Surrey is no crawler (5)
I believe the answer is:
racer
'no crawler' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'expert in middle of surrey' is the wordplay.
'expert' becomes 'ace' (ace can informally mean very good).
'in' indicates putting letters inside.
'middle of' says to take the centre.
The middle of 'surrey' is 'rr'.
'ace' put within 'rr' is 'RACER'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for racer that I've seen before include "Fast-moving snake" , "Speedway competitor, perhaps" , "one in a hurry" , "American snake" , "sportsman" .)