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In parliament’s final sitting fortnight, there’s a party on somewhere in the building most evenings.

There are multiple soirees, a legendary seafood lunch. The mood is only rarely bacchanalian – there’s usually still a heavy workload in the legislative rush to the year’s end – but it can get festive. Occasionally, politicians have been known to overindulge and disgrace themselves in late-night sittings, sometimes even making national news.

But Jacqui Lambie was not getting swept up in the good cheer this year.

“The best thing we could do,” the crossbench senator said in the penultimate sitting week, “is put drug and alcohol testing up here at Parliament House.”

Lambie, who has publicly agonised over her son’s battle with addiction, said the nation’s politicians, bureaucrats and media should lead by example and subject themselves to drug and alcohol testing. She wants welfare recipients to face a similar regime. “Mining companies do it, construction companies do it,” she said. “Let’s hit this hard … otherwise, we’re always going to have drug and alcohol problems.”

“We have almost the reverse of the situation that occurred under Abbott, which was very little communication. And now we’re probably on the verge of having more than we need.”

Although neither the federal government nor opposition rushed to endorse Lambie’s proposal, it was a timely reminder that the crossbench in this senate is anything but predictable.

Malcolm Turnbull soars high in the polls but he still has to deal with the vicissitudes of an erratic upper house.

His own house is also not in perfect order. Special Minister of State Mal Brough came under growing pressure this week from Labor after the Australian Federal Police raided his home as part of their investigation into allegations he illegally obtained a copy of Peter Slipper’s diary when he was preparing to seek preselection in the former speaker’s seat of Fisher. Brough maintains he has done nothing wrong.

There were chaotic scenes in the senate on Thursday as Cory Bernardi and Eric Abetz crossed the floor on a motion on partial voluntary student unionism. This was within their rights as backbenchers, said Turnbull, adding that the Liberals were “a party of freedom”.

But it is increasingly clear Turnbull’s internal critics are not going to lie low and leave him clear air to govern. Instead, they are holding regular powwows with ousted leader Tony Abbott and peppering the nation’s newspapers with provocative opinion pieces, all the while agitating for their allies to be given more power.

So stratospheric are Turnbull’s approval ratings, and so dismal are Labor’s, that it would be premature to say reality is beginning to bite for the newish PM. But perhaps it is starting to nibble, amid serious global security concerns and worsening economic conditions. This week, Treasury revealed it had cut the projected economic growth rate from 3 per cent to 2.75 per cent, flagging deeper deficits and casting a pall over the midyear budget update, due mid-December.

Two meetings in different parts of Parliament House on Tuesdays of sitting weeks embody the internal tensions and external parliamentary challenges facing Turnbull’s government.

In the “monkey-pod” room near the ministerial wing, Abbott and other conservatives meet regularly for a takeaway lunch and to discuss issues concerning them. The room is next to Immigration Minister Peter Dutton’s office and he hosts the lunch, according to a report this week in The West Australian. These lunches have been a fixture for years, say MPs, but the numbers have grown since Abbott was ousted in September.

1 . Push by Abbott allies

Of late, there has been a push by Abbott allies, notably backbencher and former brigadier Andrew Nikolic, to get Dutton back on the powerful national security committee of cabinet.

Turnbull has demoted Dutton from being a permanent member of the committee to being brought in as needed. This leaves the committee dominated by moderates, to the chagrin of the conservatives, who see national security as one of Turnbull’s weaknesses.

Issues the Abbott conservatives discussed over lunch this week included the terrorist attacks in Paris and the need for better vetting of Syrian refugees.

Delivering a national security statement in parliament this week, Turnbull implicitly rebuffed calls in recent opinion pieces from Abbott and his allies for the deployment of ground troops in Syria.

Turnbull also struck a markedly different tone to his predecessor. “This is not a time for gestures or machismo. Calm, clinical, professional, effective. That’s how we defeat this menace,” he said.

Dutton dismissed suggestions the lunches, first reported in Fairfax Media, could be characterised as a “resistance movement”.

“I’ve been going to Tuesday lunch for about 14 years,” he said. “For as long as I’ve been in parliament, I’ve gone to a Tuesday lunch with colleagues and friends.”

He pointed out that the “monkey-pod” room, which is sometimes used for media briefings, is located between his office and that of Christopher Pyne, a leading moderate. “I think if there was some underground movement by the Right that we wouldn’t be holding a lunch in a meeting room beside Christopher Pyne’s office,” Dutton said.

2 . Crossbench meetings

But if these conservative MPs are feeling sidelined by Turnbull, the same could not be said of those attending another Tuesday meeting, over on the senate side. In the meeting room recently allocated to the crossbenchers, the sole remaining Palmer United Party senator, Dio Wang, chairs a gathering open to the eight crossbench senators, to discuss their views on legislation and hear from the government about its plans.

“Dio is acting as chair,” says Liberal Democrats senator David Leyonhjelm. “He’s the convener of the meetings, trying to herd the cats. He’s well suited to that. He’s a gentle, obliging sort of a guy.”

Wang says his office co-ordinates the meetings “but this does not indicate any controlling influence”.

“The meetings are an efficiency mechanism for consideration of legislative matters,” says Wang. “They do not represent a voting bloc or requirement for consensus but rather serve to facilitate the cross-flow of information.

“Attendance at the meetings varies pending the workload in a particular sitting period. Everyone is very busy in Parliament House – particularly the crossbench.”

His former PUP colleagues, Lambie and Glenn Lazarus, are wary of the meetings and are not regular attendees.

Turnbull has already taken time to woo the crossbenchers. Indeed, so intense is the government’s attention that some feel it is a bit excessive. “We have almost the reverse of the situation that occurred under Abbott, which was very little communication,” says Leyonhjelm. “And now we’re probably on the verge of having more than we need.”

He says crossbenchers are now considering knocking back some of the ministers who have requested weekly meetings.

On Monday mornings of sitting weeks, Leyonhjelm says that he, Wang, and Family First Senator Bob Day already meet Finance Minister Mathias Cormann, who is deputy leader of the government in the senate. Now the government’s senate leadership team, of Cormann, George Brandis and Mitch Fifield, has offered to meet all the crossbenchers each Tuesday, but they are yet to accept this offer. It’s part of the government’s new strategy of trying to avoid senate ambushes.

“The government is not putting stuff up if it knows it will be knocked down,” says Leyonhjelm. “When Eric [Abetz] was running the senate, it was more inclined to put it up and see what happens. Now they’re counting the numbers and making sure they’re either definitely or fairly likely to win before it comes to a vote. If they don’t think they have the numbers, they don’t bring it on.”

But despite the government’s recent charm offensive, the upper house is still capable of surprising. Coastal shipping legislation was blocked on Thursday and twice recently the government’s agenda has been hijacked by opposition and crossbench senators, insisting on unplanned changes to legislation. On both occasions, the manoeuvring has been led by the Greens – and backed by Labor and some of the eight crossbenchers.

It’s a deliberate Greens strategy to force the government’s hand and put pressure on Turnbull, reviving the sort of “coalition of common sense” senate alliance that a year ago torpedoed the government’s changes to the regulation of financial advisers.

“We’re looking for opportunities on government legislation to put up amendments and put the ball back in Turnbull’s court,” says one Greens source.

The amendments may bear scant relation to the government’s proposed legislation. For instance, two weeks ago, Greens senator Peter Whish-Wilson spotted an opportunity when the government sought senate support for a crackdown on multinational tax avoiders.

This is backed by all parties, but Whish-Wilson, working with Labor’s Sam Dastyari, saw a chance to push for an unrelated tax change. Along with Labor and four crossbenchers, they gazumped the government by passing an amendment to force the disclosure of tax paid by about 800 big private companies. This sought to unwind an earlier government move to continue to shield the companies from disclosure.

The lesson here is that, even when the government can marshal senate support for its legislation, it will not necessarily pass in its preferred form.

A standoff looms since the lower house has rejected the senate’s amendments.

This week, the Greens senator, Sarah Hanson-Young, used legislation that closes loopholes on boat turn-backs and on the deportation of people whose visas are cancelled on character grounds to push for an overhaul of immigration detention.

The Greens, Labor and five crossbench senators – John Madigan, Nick Xenophon, Ricky Muir, Leyonhjelm and Wang – surprised the government with the move on Monday. Lambie and Lazarus did not vote on the amendments. Day sided with the government.

The changes were aimed at accelerating the release of children from immigration detention; reversing the secrecy provisions of the Border Force Act; requiring mandatory reporting of abuse; and allowing journalists access to detention centres, including on Nauru and Manus Island.

In both instances, the amendments – which were unacceptable to the government – were appended to legislation the government is eager to see passed.

This will test Turnbull’s willingness to compromise if the senate insists on the amendments when the legislation returns to the upper house.

Still, there are also opportunities for the government in the senate, with a Greens leader who is open to compromise. The government this week relied on the Greens to deliver support for lowering the threshold for scrutiny of foreign investment in farmland to $15 million. In exchange, the Greens secured the promise there would also be a register of foreign ownership of water assets and consideration given to increased scrutiny of foreign purchases of water.

The Greens’ opportunistic senate strategy suggests they have adopted Turnbull’s mantra of agility. It’s an attribute the prime minister will need as he deals with internal tensions and external challenges.

When Turnbull hosts his end-of-year Christmas drinks next week, the celebration may also be tinged with trepidation.