This is an area of debate and subject to great legal debate at present.
Article 50 says any EU member state can leave “in accordance with its own constitutional requirements”.
Without Parliament’s backing any prime minister invoking Article 50 without Parliamentary approval would be exercising what are known as prerogative powers. These are a collection of executive powers held by the Crown since medieval times and now reside with HM Government. These powers are often used in foreign affairs Parliament has largely left to the government. Case law establishes these executive powers cannot trump an act of Parliament.
It is therefore argued that under our constitutional settlement, the prime minister cannot issue a notification under Article 50 without being given authority to do so by an act of Parliament.
This is an issue which will require significant legal debate by specialists to determine the exact process for the Prime Minister to be able to withdraw from the EU.
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