Scott Ludlam was scouring his memory, looking for a word.

The Greens senator was grilling Government officials about why Australia had decided not to take part in nuclear disarmament negotiations, but a word was eluding him.

Finally, he landed on it.

"I remember the word we were referred to by," he said.

"Weasels. They called us weasels.

"Did other delegates refer to the Australian delegates as weasels?"

It was an unusual question, but officials from the Department of Foreign Affairs and Trade (DFAT) sitting opposite the Senator did not look confused. They knew exactly what he was talking about.

And the exchange that followed briefly illuminated the most recent global negotiations to end nuclear weapons — and Australia's role in them.

What's the new agreement?

Right now, more than 120 nations are trying to introduce a ban on nuclear weapons.

A United Nations panel has now released a draft treaty. States who sign it would be forbidden from developing or manufacturing nuclear weapons. They would also have to get rid of any weapons they already possess.

The treaty's champions argue the proliferation of nuclear weapons is an existential threat to humankind. And they say the woeful pace of global disarmament proves there is a compelling need for a new agreement that would exert moral pressure on states to disarm.

But there are plenty of problems.

First, none of the nine nuclear powers — including the US, Russia, China and the UK — support the new treaty.

Neither does Australia. The Federal Government has refused to take part in the treaty negotiations.

Why does Australia oppose the ban treaty?

North Korea has been publicising regular missile tests. ( Reuters/KCNA )

First, Australia argues that the treaty ignores geopolitical reality. Hardheads in the Government say that while everyone would like to see a world without nuclear weapons, the strategic environment is actually becoming more volatile and dangerous.

They argue the US nuclear umbrella provides vital deterrence, and protects Australia.

For example, DFAT talking points obtained by the International Campaign to Abolish Nuclear Weapons (ICAN) say Australia "must be realistic about the environment in which we operate — North Korean provocations and nuclear tests are a case in point".

Loading...

The department also said the new treaty will not actually reduce nuclear weapons, because none of the nuclear powers are on board. It argues that pushing ahead with this agreement will just drive a deeper wedge between countries who have nuclear weapons, and those who don't.

Instead, Australia's championing what's called a "building blocks" approach. We think it would be better to press nuclear states to be more transparent about their arsenals and dismantle facilities which are used to produce fissile material.

Critics are quick to point out that these sort of ideas have been pursued for decades, but disarmament remains a pipe dream.

Why were we called the weasels?

Because some countries — fairly or not — became convinced that Australia was doing everything it could to sabotage the treaty from the inside.

Australia had always made it clear it had problems with a ban, but our officials still took part in a preliminary series of negotiations. This was done through the UN Open-Ended Working Group, which met throughout 2016 to try and hammer out a draft text.

It all came to a head in August last year at the United Nations in Geneva. When it became clear that most countries in the working group were still intent on pushing ahead with a ban, Australia took to the floor and called for a vote.

Australia and its allies lost the vote, but our approach infuriated several other countries who had been pushing for a ban. They accused our officials of using the working group to deliberately undermine the agreement while pretending to search for consensus.

And it was this dispute that provoked Senator Ludlam's unorthodox questions to officials from the DFAT during Senate estimates.

Sorry, this video has expired DFAT officials grilled over whether they were 'weasels' in nuclear disarmament negotiations. ( Stephen Dziedzic )

"Is it your view that Australia participated in the working group in good faith? Because we were treated as saboteurs," Senator Ludlam asked.

The diplomat in the firing line was Richard Sadleir, a senior diplomat.

He insisted Australian negotiators were using the process to try and reshape the agreement, not destroy it.

"Senator, right up to the wire … we were acting in good faith trying to get the right outcome for Australia," Mr Sadleir said.

Senator Ludlam was quick to fire back with: "Which is to crash the working group so it didn't come up with a resolution?"

Mr Sadlier replied: "Senator, it wasn't to crash the working group, it was to get a balanced text … where the views of a ban treaty was balanced with the views of a building blocks approach."

That is when Senator Ludlam asked if Australian diplomats had been labelled weasels.

Mr Sadleir hesitated.

"Senator I'd certainly seen that term used in material," he replied.

"I'll take that as a yes," Senator Ludlam said.

What is the fallout for Australia?

Australian officials say they have no regrets about the stance they took. They argue the combative nature of the working group proved how polarising the negotiations have been. In their mind, that is more evidence that the new treaty will never deliver a consensus, or draw in nuclear states.

There's another question: will the dispute damage Australia's reputation at the United Nations?

The Government has been quick to play down that suggestion. One close observer said the term "weasel" was "thrown about", but insisted it was aimed at several nations that voted against the treaty, and not Australia alone.

As you would expect, there's been plenty of reflection in the wake of the whole episode. One cable sent from our embassy in Geneva said Australia's decision to bring on a vote was a "crunch point" that "focused minds on some uncomfortable realities".

But the cable argues that it would have all come to a head anyway at the main negotiations in New York later that year. It also says that bringing on a vote "was the logical path to follow" because the draft treaty was "consistently skewed against us."

Anti-nuclear campaigners are scathing.

"Australia's disruptive behaviour at the working group only served to isolate us from the vast majority of nations who are now working to ban nuclear weapons at the United Nations," said Gem Romuld from ICAN.

"Australia's moves backfired when the working group voted overwhelmingly in support of a ban; it was a wake-up call for DFAT.

"Australia is standing with the Trump administration and clinging to the dangerous concept that these weapons of mass destruction make us safe."

What happens now?

The champions of the new treaty are pressing ahead with the agreement.

Mr Sadleir said Australia would monitor the negotiations via video link, but the nuclear powers are still outside the tent and Australian officials suspect the treaty will go nowhere.

Some call that a tragedy, while others say it's just the reality of the world we live in.

It could be both.