Have untold pride in the first instance and confess (3,2)
I believe the answer is:
own up
'confess' is the definition.
(I know that own up is a type of confess)
'have untold pride in the first instance' is the wordplay.
'have' becomes 'own' (synonyms).
'in the first instance' indicates taking the first letters.
The initial letters of 'untold pride' is 'up'.
'own'+'up'='OWN UP'
'and' is the link.
(Other definitions for own up that I've seen before include "Confess, acknowledge fault" , "Come clean (about wrongdoing)" , "Accept responsibility" , "be honest" , "Admit to wrongdoing" .)