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.

“As far as I have been able to ascertain, his formal membership of the Liberal Party was not public knowledge, and in the circumstances there was no particular reason for the program to be alerted to the need to ask this question,” Alan Sunderland, the ABC’s head of policy, told Crikey. “Of course, had we known he was a party member, we would most certainly have made that clear during the interview, given the nature of his comments.”

In the Lateline interview, Corbett said: “I think if they come undone in these elections it would have been much better that they come undone with Julia Gillard leading them than Kevin Rudd.” He also said the Liberal Party’s paid parental leave scheme may be of just as much value as the national disability insurance scheme.

When asked if the Corbett case should prompt a rethink about the vetting of ABC guests, Sunderland said: “We always take time to reflect on any issues like this when they arise, but at this stage I remain of the view that a requirement for every interviewee to be asked whether they are personally members of a political party would be impractical and excessive.”

ABC programs such as News Breakfast have also grappled with the question of whether guests should disclose their membership of political parties.

“Our accuracy standards in the editorial policies do require us to present factual content in an accurate context, which means at times we need to label or otherwise contextualise comment,” Sunderland said. “But there are all manner of undisclosed connections, interests, agendas and organisational links that individuals may have — both political and non-political. It is just not possible to exhaustively investigate them all on every occasion. Common sense, reasonable efforts and good faith are the key.”

Former Media Watch host Jonathan Holmes told Crikey: “In an ideal world you would ask a guest beforehand whether they are a member of a political party and if it becomes relevant during the interview it should be declared … perhaps it should be more routine than it is.”

But Holmes adds it would be a shame if people who are members of political parties become excluded from debate. Many people also have strong political biases, he notes, but are not members of political parties.