This is one of the most important constitutional cases in generations. It discusses the delimitation of powers in a constitutional order without a codified constitution. The Supreme Court has upheld the decision of the High Court by ruling that the Government cannot use its prerogative power to trigger Art 50 TEU. The Parliament has to pass legislation. The reason being that the prerogative power cannot be used in order to abrogate rights that have been conferred on individuals. Interestingly, the Supreme Court unanimously also decided that it is not for the courts to police the Sewel convention and thus the devolved legislatures do not have to be consulted with regard to Brexit.
The political consequence of today’s judgment is that the Government loses part of its control over the Brexit process. Although the Parliament will not block Brexit, they can amend the Government's bill in order to exercise some control over the process. However, by not asking the Government to consult the devolved legislatures, the timetable that Theresa May has set, still seems realistic.
Politically speaking, this is a difficult moment for the government. However, this decision should not be understood as an outright win for Remain. The question for the court was not whether the UK should or should not withdraw but what is the appropriate procedure for triggering the withdrawal procedure. It is a strong reminder, however, that the government should respect the constitutional rules during the Brexit process. At the end of the day, Brexit would lead to a fundamental change in the British constitutional order. In a system of parliamentary sovereignty, it seems constitutionally appropriate that Westminster will have a say in this process.
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