London: Britain's highest court has ruled that Parliament – not the government – must fire the starting gun for Brexit.
The decision means both houses of Parliament will have the chance to debate, and potentially even block, the triggering of the 'Article 50' clause in the European Union constitution that starts Britain's withdrawal.
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UK can't trigger Brexit without parliamentary vote
The UK's Supreme Court has ruled that Prime Minister Theresa May must get parliamentary approval before leaving the European Union.
Prime Minister Theresa May has said she wants to trigger Article 50 by the end of March, so negotiations over the terms of Brexit can begin.
The government is expected to introduce legislation quickly that will get the required parliamentary nod.
There is speculation of a significant rebellion among anti-Brexit MPs, especially Labour, but the vote is expected to pass easily with the support of nearly all Conservative MPs.
It could hit more resistance in the House of Lords.
The case was one of the most significant legal battles of a generation.
It was a rerun of England's centuries-old historical divide, pitting the fading powers of the monarchy, wielded by the government, against the supremacy of Parliament.
![British Prime Minister Theresa May faces another hurdle before she can pull Britain out of the EU.](/web/20170126042903im_/http://www.theage.com.au/content/dam/images/g/t/x/q/e/7/image.related.articleLeadwide.620x349.gty0xy.png/1485317672564.jpg)
The case was brought by an investment manager, Gina Miller and a hairdresser, Deir Tozetti Dos Santos, whose lawyers argued that the government's prerogative powers could not alone take away the rights of British citizens conferred by the EU over four decades of membership, and confirmed by the British Parliament.
It was heard by all 11 justices of the Supreme Court over four days in December.
![Lord Neuberger, President of the Supreme Court, centre, delivers the judgment in London on Tuesday.](/web/20170126042903im_/http://www.theage.com.au/content/dam/images/g/t/y/1/p/k/image.related.articleLeadwide.620x349.gty0xy.png/1485317672564.jpg)
They agreed by an 8:3 majority that the government could not trigger Article 50 without Parliament's consent.
Lord Neuberger, the president of the Supreme Court , delivered the judgment to a packed courtroom.
![Labour Leader Jeremy Corbyn said his party would not frustrate the process for invoking Article 50.](/web/20170126042903im_/http://www.theage.com.au/content/dam/images/g/t/y/1/p/t/image.related.articleLeadwide.620x349.gty0xy.png/1485317672564.jpg)
"We cannot accept that a major change to UK constitutional arrangements can be achieved by ministers alone; it must be effected in the only way that the UK constitution recognises, namely by Parliamentary legislation," Lord Neuberger said in the judgment.
"Prerogative powers cannot be invoked to withdraw from the EU Treaties."
The court also held, unanimously, that the devolved parliaments of Scotland, Wales and Northern Ireland did not have a right of veto.
They were judging an appeal on a previous decision by Britain's High Court, which endured angry attacks in the media for supposedly thwarting the democratic will of Britain in last year's Brexit referendum.
In response to the judgment a spokesperson for the prime minister said the government would trigger Article 50 as planned by the end of March.
"Today's ruling does nothing to change that," the statement said.
David Davis, Secretary of State for Exiting the European Union gave a statement and answered questions in Parliament following the decision on the process for triggering Article 50.
He said the government would introduce legislation to start the formal process of the UK withdrawing from the EU.
It would be a straightforward bill, that will not be about whether the UK should leave the EU, "because that decision has already been made", Mr Davis said.
He added, to cheers from his government colleagues: "I trust no-one will use it as a vehicle for attempts to thwart the will of the people or to frustrate or delay the process."
Labour leader Jeremy Corbyn said he would use the Article 50 vote to try to force the government to back down from some of its Brexit aims, particularly its threat to lower corporate taxes if Europe doesn't agree to a new free trade deal with the UK after Brexit.
He said his party "respects the result of the referendum… and will not frustrate the process for invoking Article 50".
But he added that "Labour will seek to amend the Article 50 Bill to prevent the conservatives using Brexit to turn Britain into a bargain basement tax haven."
"Labour demands a plan from the government, accountability to Parliament throughout negotiations and a meaningful vote on the final deal."
Several MPs used the debate to call for the government to issue a 'white paper' outlining its aims for the Brexit negotiation, and its trade plan for a post-Brexit Britain.