The U.K.’s High Court in November 2016 ruled that the British government could not trigger Article 50 of the E.U. Treaty, thereby setting off Brexit negotiations, without having Parliament voting on the matter first.

The government has appealed the decision and the appeal will be heard in the U.K. Supreme Court in early December. The court stated it would deliver its judgment, which is final, “probably in the New Year.” These developments may prevent Prime Minister Theresa May from triggering Article 50 before the end of March 2017, as was her stated intention until now.

Should the judgment be affirmed, a bill will need to be passed by the House of Commons and the House of Lords that approves starting Article 50 negotiations. This means that British MPs will not have an opportunity to vote on a Brexit “deal” but only on triggering negotiations. The process of negotiating an exit deal between the U.K. and the E.U. has not yet begun—and it cannot begin until Article 50 is triggered.

The majority of MPs favored remaining in the E.U. and therefore some observers speculate that Article 50 may never be triggered, preventing Brexit from happening at all. However, many MPs may decide that the result of the referendum means they should allow the government to begin the exit process without delay. There is no precedent for this situation in U.K. constitutional law and the High Court had to draw on case law dating back to 1610 for applicable underlying principles of the constitution.