What to Know About the British Court's Ruling on Brexit

— -- Today, the High Court in the U.K. ruled that Britain's Parliament has to vote on whether the United Kingdom can leave the European Union.

U.K. Prime Minister Theresa May, who was elected in the wake of the British vote to leave the EU, said she wants to begin the formal negotiation process for Brexit by the end of March 2017.

But today’s court decision, if it stands, will not allow her government to proceed until Parliament makes its determination.

What exactly does that mean for Brexit? Here are some key facts:

Why is a court involved?

A group led by investment manager Gina Miller, which raised money for its challenge to the government through crowd-funding, launched a Brexit legal case arguing that a government shouldn’t be able to act independently and leave the EU without consulting Parliament.

The government argued that it should be able to use its royal prerogative powers, meaning it could act alone, to trigger Article 50 of the Lisbon treaty and begin the formal process to leave the EU.

Today, the government lost the case.

The people voted, why does Parliament have to vote?

Nearly 52 percent of British voters voted "Leave" the EU, while around 48 percent voted "Remain" in June. But the voters were not asked about what leaving the EU should entail and how the process should be carried out.

"People gave consent to leave the EU. They did not say exactly how the government will interpret it," Dr Peter Paul Catterall, Reader in History, Sociology and Criminology at the University of Westminster, told ABC News. "The referendum shouldn’t give the government carte blanche to how they interpret it. They’ve been interpreting their mandate to mean a series of other things which people didn’t vote on. How is that democratic?"

"The court ruling stops the government from establishing a very dangerous precedent that they can set up referendums and then interpret them the way they want," he said.

What happens next?

The government is appealing today’s decision to the Supreme Court. A hearing is expected next month.

"I expect the Supreme Court may affirm the judgement of the High Court because from what I’ve seen from the judgment I can’t see grounds on which they will find an alternative interpretation," said Catterall.

If the Supreme Court upholds the High Court’s decision, the government might be able to appeal the case to the European Court of Justice. But that is still unclear.

If the government loses its appeal and accepts the Supreme Court’s decision, Members of Parliament (MPs) will vote on whether Article 50 should be triggered and when it should happen.

Why is the ruling significant?

It could sink Theresa May’s hopes of triggering Article 50 by the end of March. "Even if Parliament eventually votes to start Article 50, that could take months and so delay the start of formal negotiations between the U.K. and the E.U.," Tim Oliver, Dahrendorf Fellow at the London School of Economics and visiting scholar at New York University, told ABC News.

What does this mean for Brexit?

It is unlikely that MPs will try to block the referendum result, even if they are against leaving the E.U. But the government will have to give the Parliament much more information about the process, which may be delayed as a result.

"Brexit will still happen in some way, but when and how will now take longer than May had hoped," Oliver said, adding that this may not be bad because the government is not yet ready to negotiate Brexit.

"They don’t have the people in place or the ideas as to what to negotiate with the E.U. and others. Plus the rest of the E.U. is in no position to negotiate because the main deals will only happen after the French and German elections."

Why does Brexit matter for the U.S.?

It is in the U.S.'s interest that the U.K. remain strong, stable and has a good relationship to other European countries. Brexit may push the country into turmoil, Oliver said.

"The U.K. is one of the U.S.'s closest allies," he said. "The British vote to leave the E.U. has the potential to tear apart the country, radically change its political and economic landscape, consume the time and effort of its political class for several years, add to growing tensions between it and its closest allies in Europe and around the world, and generally cause a crisis that is more often the result of revolution or defeat."

Editor’s note: An earlier version of this story incorrectly stated that it was the ‘Supreme Court’ that had made the ruling, a mistake that came in during the editing process. This has since been corrected to note that it was the ‘High Court’ of the UK.