The U.K.'s exit from the European Union must be triggered by Parliament, not by the prime minister, the nation's Supreme Court says. In an 8-3 ruling, the court ruled that Theresa May doesn't have legal standing to carry out Brexit, the plan to leave the EU that voters embraced in a close referendum last June.

The prime minister's office says the ruling "does nothing to change" its timetable of leaving the economic union by the end of March. That's when May set a deadline for invoking Article 50 — the exit clause that's built into the EU's constitutional rules. But the already complicated process, the Supreme Court now says, must also include Parliament.

"The ruling is an embarrassing setback for the prime minister, but it does not threaten to derail Brexit," NPR's Frank Langfitt reports from London. "Ministers of Parliament can delay the bill and debate it, but they can't overturn the June referendum."

The ruling bolsters a High Court ruling from November, which Prime Minister May's government had appealed. It's also a victory for Gina Miller, a leading plaintiff in the case who works as an investment manager.

Saying that her case was about the legal process, Miller said after today's ruling, "No prime minister, no government, can expect to be unanswerable or unchallenged."

In an interview with NPR last year, Miller explained her reasons for challenging the government's plan to leave the EU:

"Because I don't feel that we've had a rational, grown-up, sensible debate about all the factors that would impact on us leaving the EU. It was very much overshadowed by people who were basically power hungry politicians who were fooling the public, in my view."

In that interview, Miller added that people who pushed to leave the EU "didn't have a plan" for what comes next after leaving the union. And today, she acknowledged that the issue was one of the most divisive in modern times in Britain.

Responding to Tuesday's ruling, No. 10 Downing St. noted that Parliament had previously backed the idea of Brexit when it approved the plan to hold a public referendum.

A government spokesperson issued this statement:

"The British people voted to leave the EU, and the government will deliver on their verdict — triggering Article 50, as planned, by the end of March. Today's ruling does nothing to change that."It's important to remember that Parliament backed the referendum by a margin of 6 to 1 and has already indicated its support for getting on with the process of exit to the timetable we have set out."We respect the Supreme Court's decision, and will set out our next steps to Parliament shortly."Copyright 2017 NPR. To see more, visit