Very important bloke, top dog at summit! (6)
I believe the answer is:
urgent
'very important' is the definition.
'top dog at summit' is the wordplay.
'top' means to remove the first letter.
'dog' becomes 'cur' (cur is a kind of dog).
'at summit' becomes 'gent' (I can't justify this - if you can you should believe this answer much more).
'cur' with its first letter removed is 'ur'.
'ur'+'gent'='URGENT'
'bloke' is the link.
I am not very happy about this link. It may be part of another bit of the clue.
(Other definitions for urgent that I've seen before include "demanding speedy action" , "Critical" , "Pressing, imperative" , "Pressing, immediate" , "Extremely pressing" .)