Refuse dumped beside northern motorway, last of all (4)
I believe the answer is:
deny
'refuse' is the definition.
(I know that refuse can be written as deny)
'dumped beside northern motorway last of all' is the wordplay.
'last of all' indicates one should take the final letters.
The last letters of 'dumped beside northern motorway' are 'DENY'.
(Other definitions for deny that I've seen before include "Refute, contradict" , "Refuse to admit the truth" , "Declare not to be true" , "Claim to be untrue" , "Disown" .)