The ABC has defended its decision not to grill Fairfax chairman Roger Corbett about his political leanings before a Lateline interview this week, saying it would be "impractical and excessive" to quiz every guest on their politics.

In the Lateline interview on Tuesday, Corbett, who is also a board member of the Reserve Bank, blasted Prime Minister Kevin Rudd for undermining Julia Gillard during her leadership. It was revealed the next day that Corbett is a member of the Liberal Party.