(Bloomberg) -- Rishi Sunak backed the winning side in the UK’s pivotal vote to leave the European Union, fueling a rise that ultimately made him premier. Now he’s fighting to avoid becoming the latest Conservative leader consumed by the resulting civil war in the governing party.

The British prime minister faces a crucial two weeks if he is to control feuding Tory Members of Parliament and lead them into a general election expected next year. The latest fight is about whether the government should bend or ignore domestic and international laws so the UK can deport asylum-seekers to Rwanda without considering their claims.

But the schism runs far deeper, posing existential questions about the Conservative Party, the relative power of the House of Commons, the House of Lords and the judiciary, as well as UK sovereignty and its place in the world.

When lawmakers vote Tuesday on the anti-immigration legislation Sunak says will get Rwanda deportation flights in the air, those old Brexit dividing lines, tactics and risks that brought down former Prime Minister Theresa May will return to the fore. That contradicts the political brand he’s tried to build since taking power last year following the chaotic premierships of May’s successors, Boris Johnson and Liz Truss: stability after years of turmoil.

“Brexit is undoubtedly the origin of this, but actually the split has got much worse,” former Attorney General Dominic Grieve, who backed Remain in the 2016 referendum and was ejected from the party in 2019 after rebelling against Johnson, told BBC TV. “What we’re now watching is a split between people who believe in the rule of law and people who don’t.” 

The Rwanda plan has been controversial since it was announced by Johnson in 2022, and has been repeatedly held up by European and UK courts. Persistent questions about value for money will intensify after it emerged this week the UK has spent £100 million ($126 million) on the plan this year, on top of the £140 million previously paid out — before any flights have taken off.

Rather than drop it, Sunak and his team have embraced a policy they see as a way of reversing the Tories’ low standing in the polls. 

It is intrinsically linked to one of the five pledges Sunak wants voters to judge him by, to stop asylum-seekers arriving in small boats across the English Channel. Ministers see the Rwanda deportation program as a necessary deterrent, even as they tried to convince the courts that the African nation is a safe place to send deportees. The UK Supreme Court decided last month it isn’t, ruling Sunak’s plan unlawful and triggering the Tory disarray.

Like the wrangling over Brexit, the issue is becoming one of political purity, especially for right-wing Tory MPs. There is considerable overlap between the lawmakers who demanded the hardest possible divorce from the EU and those demanding Sunak override UK law and take Britain out of the European Convention on Human Rights so asylum-seekers have no legal venue to appeal.

Just as in those heated post-2016 Brexit years, there are also Tory MPs deeply uncomfortable with the UK turning its back on international obligations and overriding laws for political gain.

“If there’s any prospect of any British bill or act of Parliament bypassing international law, then I will not support it,” Tobias Ellwood, who has advocated the UK rejoining the EU single market, told Times Radio. “We uphold international law. We don’t break it.”

There was a moment Wednesday when Sunak appeared to have threaded the needle between the rival camps. A new treaty with Rwanda ministers said guaranteed deportees couldn’t be forcibly moved back to their home countries, coupled with legislation to dis-apply elements of UK human rights law and declare Rwanda “safe,” would allow flights to proceed, he promised.

Members from both factions emerged from a meeting with Sunak broadly expressing satisfaction.

But the relative calm vanished dramatically with the resignation of immigration minister Robert Jenrick, taking Downing Street by surprise. People familiar with the matter said the impact was immediate on both sides of the argument. 

On the right, where there is barely disguised positioning to succeed Sunak, Jenrick’s resignation prompted a race to ensure he didn’t steal a march by appearing the most hard-line on immigration. Their response was straight out of the Brexit playbook, with MPs referring analysis of the legislation to a self-described “star chamber” of like-minded lawyers.

At the same time, more centrist Tories were angry that having made concessions to help Sunak keep right-wing colleagues onside, Jenrick quit anyway. Their mood darkened further when a tense and combative Sunak used a hastily arranged press conference to try to get right-wing MPs onside by talking up his bill’s hard-line anti-immigration elements.

That One Nation group of moderate Tories will also consult lawyers before deciding how to vote, a person familiar with the matter said. Some are nervous about how much power is handed to ministers, they said.

That all means Sunak faces a dangerous period as he tries to get MPs onside. In a sign of how uncertain he is about the potential size of any rebellion, the premier decided not to make Tuesday’s vote one of confidence in his government. That would dramatically raise the stakes, to the point where if he lost, he’d face intense calls to resign or call an election. 

Sunak said he’d like the bill to become law in “record time,” suggesting he’ll try to complete its Commons passage before the house breaks on Dec. 19 for its Christmas recess, setting up a battle in the Lords next year.

Given how totemic the Rwanda plan has become, the stakes are high regardless of the vote’s status. It’s far from clear Sunak’s opponents on the right have the numbers to oust him, while there’s no desire to do so on the Tory left.

But just as Tory wrangling over Europe weakened premiers from Margaret Thatcher and John Major to David Cameron and May, so Sunak — even as a committed Brexiteer — is struggling to tame the party’s internecine conflict.

“The Tory civil wars have completely reopened,” ex-Tory Chancellor George Osborne said on his Political Currency podcast. “Rishi Sunak’s big claim was, ‘I’ve come after the chaos of Boris Johnson and the chaos of Liz Truss… I’ve stabilized things.’ He can’t now claim anymore to have stabilized things. His government is fragmenting around this immigration issue.”

(Updates with cost of Rwanda plan in sixth paragraph.)

©2023 Bloomberg L.P.