SAN FRANCISCO (Diya TV) — The British government’s plan for leaving the European Union was thrown into uncertainty Thursday after a High Court ruled that Parliament must first hold a vote before the process can officially begin.

The referendum was approved by nearly 52 percent of voters during last June’s election. Thursday’s ruling will likely only serve to slow, not halt, the withdrawal proceedings.

Regardless, the court’s decision serves as a significant blow to Prime Minister Theresa May, who had already begun planning steps to leave the European Union by the end of March. While the government immediately vowed to appeal the court’s ruling, May’s plan could have already been thrown into disarray, analysts said.

She would be forced to work with Parliament and consider its competing priorities for Britain’s future. Specifically, she would have to give it a detailed strategy for negotiating the British departure, or “Brexit.” She has adamantly resisted doing so, arguing that this would impede her flexibility in the negotiations, preventing Britain from getting the best possible deal.

Very few believe Parliament would attempt to blockade the withdrawal from the union, multiple English lawmakers have already vowed to uphold the referendum and pledged to abide by the results.

The ruling has also unsettled proponents of the withdrawal, who warned against any backsliding. Nigel Farage, who resigned as leader of the nationalist U.K. Independence Party after the referendum, said he feared that Britain was heading for a “half Brexit,” and he said he would return to politics in 2019 if the country had not left the bloc by then.

“I see M.P.s from all parties saying, ‘Oh well, actually we should stay part of the single market; we should continue with our daily financial contributions,’ ” he said in an interview on BBC Radio. “I think we could be at the beginning, with this ruling, of a process where there is a deliberate, willful attempt by our political class to betray 17.4 million voters.”

On Thursday, the government said that an expedited appeal would be heard in December by the Supreme Court, Britain’s highest appellate body, and that it was sticking to its timetable for leaving the bloc for now.