A strange moment played itself out this morning at the Senate Foreign Affairs, Defence and Trade Committee estimates hearings. The Department of Foreign Affairs and Trade took the unusual step of point-blank refusing to answer questions relating to Burma’s nuclear program because the information derives from US diplomatic cables released by Wikileaks.

At the Committee hearings this morning, Greens Senator Scott Ludlam, who has doggedly pursued the Government’s reaction to WikiLeaks through Estimates, asked DFAT officers about WikiLeaks’ revelations about the Burmese régime’s nuclear program, only to be rebuffed by DFAT Secretary Dennis Richardson, who stated that the Government’s policy was “not to comment on leaks.”

But Richardson or any other official isn’t allowed to do that. Under Estimates rules, there are only three grounds for officials refusing to respond: matters of policy (which are usually handled by the Minister present), public interest immunity; and confidential material “where in camera evidence is desirable”.

The public interest immunity grounds are detailed in the Estimates guidelines, and are supposed to require a letter from the relevant Minister (Stephen Conroy was the Government’s Minister on duty at the hearing, given Kevin Rudd is the portfolio Minister) to the committee chair.

Conroy leapt in to take the question on notice, but Ludlam demanded that the Government formally indicate it was invoking public interest immunity in relation to WikiLeaks. Labor Senator Michael Forshaw intervened to note that the refusal related to the reference to leaked US cables, not WikiLeaks per se.

What’s odd about this is that the WikiLeaks material that was the subject of Ludlam’s question was not Australian Government material that was leaked (in which case, there’s at least a case for a government refusing to respond) but of course US government material.

And refusing to comment on leaks in other countries doesn’t fit within the public interest immunity guidelines. Either way, it represents a significant and very convenient extension of the existing defence against inquisitive senators.