Cornish resort has no new wharf (4)
I believe the answer is:
quay
'wharf' is the definition.
(quay is a kind of wharf)
'cornish resort has no new' is the wordplay.
'cornish resort' becomes 'newquay' (I've seen this before).
'has no' is a deletion indicator.
'newquay' with 'new' removed is 'QUAY'.
(Other definitions for quay that I've seen before include "Dock, wharf" , "Dock's loading area" , "Landing place" , "Landing area" , "crucial, by the sound of it" .)