Parliament must be allowed to vote on whether the Government can begin the Brexit process, the Supreme Court has ruled.
The judgement on the government's fast-tracked appeal means Theresa May will not be able to commence talks with the European Union until MPs and peers give their backing.
However, this is likely to occur in time for the government's March 31 deadline, as ministers are set to introduce emergency legislation into Parliament to authorise the UK's departure from the EU. Brexit Secretary David Davis promised a parliamentary bill "within days".
The Supreme Court ruled that there was no need for the government to wait for consent from the devolved assemblies in Scotland, Northern Ireland and Wales.
What was the case about?
During the Supreme Court hearing, it was argued that denying Parliament a vote was undemocratic and breached the UK's long-standing constitutional principles.
Campaigners said that triggering article 50 of the Lisbon Treaty would mean overturning UK law, so MPs and peers should be given the right to decide.
However, the government argued that it could act without consulting Parliament - citing its Royal Prerogative (powers handed by the Crown to the government).
It also pointed out that MPs had voted overwhelmingly in favour of the calling of June's Brexit referendum, putting this issue in the hands of the British public.
What was the court's view?
The Supreme Court, by a majority of eight to three, ruled that the government cannot trigger Article 50 without an act of Parliament authorising it to do so.
The court's president, Lord Neuberger, said: "When the UK withdraws from the EU treaties , a source of UK law will be cut off. Further, certain rights enjoyed by UK citizens will be changed.
"Therefore, the government cannot trigger article 50 without parliament authorising that course.”.
The court also rejected, unanimously, arguments that the Scottish Parliament, Welsh Assembly and Northern Ireland Assembly should get to vote on Article 50 before it is triggered.
Their overwhelming consensus was that relations with the EU were a matter for the UK government.
How has the government reacted?
Mr Davis told MPs he was "determined" Brexit would go ahead as voted for in June's referendum.
He said: "It's not about whether the UK should leave the European Union. That decision has already been made by people in the United Kingdom."
"There can be no turning back. The point of no return was passed on June 23 last year."
The eight-to-three margin of defeat suffered by the government was bigger than ministers had hoped for, although they had already conceded they were likely to lose.
In May’s favour, there is not a large appetite in either the House of Commons or the Lords to actively block the process.
The Scottish National Party and Liberal Democrats will probably vote against the bill if their amendments are not passed, and some Labour rebels are likely to join them. But Labour will not wish to appear to be trying to prevent the referendum result being honoured.
