Britain’s Supreme Court has ruled that the UK government must hold a vote in parliament before beginning the process of leaving the European Union. The decision is a complication for Prime Minister Theresa May, who wanted to trigger Article 50 of the Lisbon Treaty — the legal mechanism that begins the process of leaving the EU — by the end of March. Doing so would open the door for EU negotiations, which are likely to last two years. May had promised lawmakers a vote on the outcome of the talks, but wanted to begin the process without a decision in parliament.