Block up; obstruct (7)
I believe the answer is:
occlude
I believe this clue is a double definition.
'block up' is the first definition.
(thesaurus)
'obstruct' is the second definition.
(synonyms)
(Other definitions for occlude that I've seen before include "Block, obstruct" , "Cod clue to shut out" , "cover" , "Cut or shut off" , "Close up, obstruct" .)