The UK’s controversial flagship immigration policy faces its sternest test this week, when the nation’s top court will decide whether it’s lawful.

Five justices of the Supreme Court will on Wednesday issue a decision on the government’s plan to deport asylum seekers to Rwanda, the central plank of the Conservative Party’s tough immigration platform.

The ruling will either embolden Prime Minister Rishi Sunak in his efforts to prevent migrants coming across the English Channel in small boats, or cause another embarrassment for the government and resurface old arguments about the UK’s adherence to the European Convention on Human Rights.

It isn’t the first time that the Supreme Court, which sits just across from the House of Commons in Westminster, finds itself at the center of a political crisis. Its judges previously intervened on key rulings on Brexit and quashed a controversial bid by Boris Johnson to suspend Parliament.

Why does the UK want to deport refugees to Rwanda?

The Conservatives say there’s a pressing need to stop asylum seekers entering the country on small boats often in treacherous conditions and with sometimes tragic consequences. The plan to fly refugees some 4,000 miles (6,437 kilometers) to the central African nation for processing will act as a deterrent and put pressure on criminal gangs and smugglers, the government has said.

Pushing through the headline-grabbing policy is a priority for Home Secretary Suella Braverman who, in a speech at the latest Conservative Party conference, warned of a “hurricane” of mass migration and has previously said it was her “dream” to see migrants flown to Rwanda.

Despite all the rhetoric, asylum seekers are still arriving in significant numbers. The asylum caseload in the UK rose to 215,500 as of June, according to government data. Roughly 20,100 people were recorded as entering the UK on small boats between January and August 2023.

What if the Supreme Court rejects it?

Sunak’s plan to “Stop the Boats” — one of the five priorities he set out to voters ahead of a likely election next year — would be left in tatters. There is no apparent Plan B. Still, parts of the right-wing of the Conservative Party will view a loss as an opportunity to revive another battle — to reverse the UK’s membership of the European Court of Human Rights.

That constituency sees the Strasbourg, France-based court as needlessly meddling in British law. Last year the ECHR stopped the first Rwanda flight in an eleventh-hour intervention.

The tension lies in the fact that the new legislation potentially puts Britain at odds with the European court, which upholds the convention as anyone deemed to have entered the country illegally will automatically be banned from claiming asylum or citizenship. Under the old laws, courts accepted the majority of claims.

--With assistance from Stuart Biggs.