London's High Court said on Tuesday it would rule "as quickly as possible" on whether British lawmakers, and not the government alone, must trigger the formal process of leaving the European Union, in a case closely watched by politicians and markets.
Campaigners have taken legal action to argue Prime Minister Theresa May and her ministers do not have the authority to invoke Article 50 of the EU Lisbon Treaty, the mechanism by which a nation can leave the bloc, without the explicit backing of parliament.
During three days of legal wrangling involving some of the country's top lawyers, the High Court has heard from the government that a decision to trigger Article 50 could not be reversed and that it was "very likely" the final exit deal agreed with the EU would have to be ratified by parliament.
However, the key issue of whether May can invoke Article 50 using the ancient power of "royal prerogative" remains to be determined.
"We shall take time to consider the matter and will give our judgments as quickly as possible," said Lord Chief Justice John Thomas, Britain's most senior judge who has been hearing the case with two other leading justices.