A British court ruled Thursday that a U.K. government plan to send asylum-seekers on a one-way trip to Rwanda is unlawful, delivering a blow to the Conservative administration’s pledge to stop migrants making risky journeys across the English Channel.

Refugee law expert David Cantor said the ruling would “send a ripple effect more widely through this idea of sending asylum seekers to third countries.”

“Any country that might wish to enter into this kind of memorandum with the U.K. government, as Rwanda did, would equally be quite likely to be a government which had weak asylum procedures, (where) there were questions about safety in the country,” said Cantor, director of the Refugee Law Initiative at the University of London’s School of Advanced Study.

He said the U.K. “has had negotiations with many countries which do have robust court structures and asylum procedures, and there’s very little willingness there to contemplate these sorts of schemes.”

In a split two-to-one ruling, three Court of Appeal judges said Rwanda could not be considered a “safe third country” where migrants from any country could be sent.

But the judges said that a policy of deporting asylum seekers to another country deemed as safe was not in itself illegal, and the government said it would challenge the ruling at the U.K. Supreme Court.

It has until July 6 to lodge an appeal.

Even if the plan is ultimately ruled legal, it’s unclear how many people could be sent to Rwanda.

The government’s own assessment acknowledges it would be extremely expensive, coming in at an estimated 169,000 pounds ($214,000) per person.

But it is doubling down on the idea, drafting legislation barring anyone who arrives in the U.K. in small boats or by other unauthorized means from applying for asylum.

If passed, the bill would compel the government to detain all such arrivals and deport them to their homeland or a safe third country.

The U.K.’s Home Secretary on Thursday slammed a decision by a top judge to rule the government’s plans