Key Points:

CANBERRA - Now the world will never know whether outgoing United States President George W. Bush is as much of a numbskull as an alleged remark to Australian Prime Minister Kevin Rudd would suggest.

If last month's report in the Weekend Australian is true, then Bush had no idea about the organisation he will host this weekend in a bid to save the world from financial meltdown.

It would also mean that someone in the Prime Minister's office - even Rudd himself - has a motormouth of diplomatically vast proportions.

No world leader, especially not one who was a senior diplomat, can afford to breach confidence and heap humiliation on the most powerful office in the world.

So did Bush really not know what the G20 was, that it was a gathering of the world's 20 biggest economies, adding the likes of China and Brazil to the real giants that gather together as the G7?

And did he disclose his ignorance to Rudd on October 10 when, during a conversation between the two, the Australian suggested that to ensure the widest possible response, the big Asian countries should be invited to a global gathering?

According to the Weekend Australian, Bush replied: "What's the G20?"

And did Rudd let this slip?

Although Chris Mitchell, the editor of the Australian, was dining with Rudd at Kirribilli House in Sydney when the call came through, he appeared not to have been privy to the conversation.

Rudd has said that only he and a note-taker were present in the room.

Rudd, and the White House, have also denied that Bush had no idea of what the G20 was.

The only chance of finding out is now doomed.

Yesterday the Greens and independent Senator Nick Xenophon rejected a call for a Senate inquiry into the leak, concluding that the Upper House had no chance of uncovering the truth and that there were more urgent matters to discuss.

But the Opposition has been in a lather over the affair. They may have been slow on the uptake of a story that appeared on October 25, but once the potential political implications of a broken presidential confidence became clear, senior Liberals grabbed it between their jaws.

Former Liberal Party director and infrastructure spokesman Andrew Robb claimed Rudd's indiscretion was reverberating throughout the diplomatic community.

"I think as long as Kevin Rudd is Prime Minister, no world leader will have a fully frank discussion with him," Robb told Channel 10.

Pursuing Rudd during a failed censure motion in Parliament this week, Opposition leader Malcolm Turnbull accused the Prime Minister of hypocrisy in not ordering an investigation into the leak while earlier fuming over others involving the Federal Police and the Defence Department.

He said Rudd had intended embarrassing Bush through an account (of the conversation) "so self-serving that it presented himself as a diplomatic encyclopaedia, a font of all knowledge, and the President of the United States, the chief executive of our greatest ally as a fool".

More, Turnbull pointed the finger directly at Rudd.

"The Prime Minister's fingers are all over this," he said.

"Every letter, every paragraph, is dripping with his DNA."

Rudd has refused an investigation, and under heavy fire in Parliament, declined to deny that he or his staff had leaked Bush's alleged gaffe to the Weekend Australian.

To force the issue, Family First Senator Steve Fielding, supported by the Opposition, proposed that a Senate select committee inquiry be held into the integrity of Rudd's office, the circumstances of the leak, and any involvement of the Prime Minister's office.

He sought the power to force ministers, their advisers and the police to appear before the committee.

But yesterday Greens leader Bob Brown killed the proposal by denying Fielding the numbers.

"This inquiry won't get the answers that Senator Fielding is seeking," he told ABC radio.

"The Prime Minister, his staff, certainly the President of the United States and other entities are unlikely to be called before such an inquiry."