Informal discussion in party -- excellent (6)
I believe the answer is:
confab
'informal discussion' is the definition.
(I've seen this before)
'party excellent' is the wordplay.
'party' becomes 'con' (abbreviation for Conservatives).
'excellent' becomes 'fab' (slang abbreviation of fabulous).
'con'+'fab'='CONFAB'
'in' is the link.
(Other definitions for confab that I've seen before include "Chatter" , "Chat (informal)" , "Informal conversation" , "natter" , "Informal discussion (colloq.)" .)