Is Brexit coming off the rails? Months after British voters chose to leave the European Union, a big court ruling.

FOX's Simon Owen reports from London:

London's High Court ruling that the British Prime Minister does not have the power to trigger the UK's departure from the European Union without holding a vote in Parliament first.

Prime Minister Theresa May had said she'd begin the process in the next few months, and wouldn't consult lawmakers.

But campaigners including Gina Miller challenged that:

(Miller) "The result today is about all of us, it's about our United Kingdom and all our futures."

The ruling risks derailing Theresa May's timetable and makes Brexit even more complicated.

One of May's top ministers, Liam Fox, admitting:

(Fox) "The government is disappointed by the court's judgement."

But promising an appeal.

In London, Simon Owen, FOX News.

Follow Simon Owen on Twitter: @BigSo