A senior Australian public servant has penned a colourfully worded anonymous letter to Senator Bill Heffernan about being forced to wait at a Senate estimates hearing watching "you and your dipshit colleagues trying to score political points off each other".

The letter was read out during a rural and regional affairs and transport committee hearing on Monday – the same day it was reported that former Health Department secretary Stephen Duckett said estimates were disgraceful because senators had little care for the family lives of bureaucrats called to appear.

Senator Bill Heffernan during an earlier Senate estimates hearing. Credit:Andrew Meares

The letter, which started "Dear Senator Heffernan", said: