Established diary has entry for November evening, Tory leader admitted (4-8)
I believe the answer is:
long-standing
'established' is the definition.
(I've seen this before)
'november evening tory leader admitted' is the wordplay.
'november' becomes 'long' (I can't justify this - if you can you should believe this answer much more).
'evening' becomes 'sanding' (sand can mean to smooth or make even).
'leader' suggests taking the first letters.
'admitted' means one lot of letters goes inside another.
The first letter of 'tory' is 't'.
'sanding' going around 't' is 'standing'.
'long'+'standing'='LONG-STANDING'
'diary has entry for' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
(Other definitions for long-standing that I've seen before include "Having existed for some time" , "Existing over much time" , "Existing over the years" , "Existing over a considerable period" , "Well established" .)