Reaction from ITV News Political Correspondent Carl Dinnen
The High Court has ruled the Government requires Parliament's consent to trigger Article 50 and start the UK's withdrawal from the European Union.
The ruling now plunges the Government's plans for Brexit into disarray as the process of leaving the EU will be subject to full parliamentary control.
A spokesman for the Government has already said they will appeal the ruling.
Any appeal will be held in the Supreme Court from December 5-8.
Scottish First Minister Nicola Sturgeon, who is lobbying for Britain to remain in the European single market, hailed the ruling and described the finding as "significant indeed".
A statement read on behalf of hairdresser Deir dos Santos, who, alongside businesswoman Gina Miller began legal proceedings against the Government just four days after the referendum, said: "Today is a victory for everyone who believes in the supremacy of parliamentary democracy.
"I've never challenged the result of the referendum, I in fact voted for Brexit... for the sole reason that I wanted power to be returned from Europe to the British parliament.
"I did not think it was right for the Government than just to bypass Parliament and to try and take away my legal rights without consulting Parliament first".
He said: "In her speech to the Conservative Party conference [in October] the Prime Minister attacked me for bringing these proceedings as a claimant.
"She said that I was trying to subvert democracy - that it was an unwarranted and irresponsible attack. As is my constitutional right, I sought the protection of the court to stop unlawful Government action.
"The court has now given me that protection.
"I now hope that everyone will respect the courts decision so that Parliament will now make a decision in relation to the service of the Article 50 notice".
Mrs Miller added: "This case was about process, not politics.
"The result today is about all of us. It's not about me or my team. It's about our United Kingdom and all our futures.
"It's not about how anyone voted. Every one of us voted for the best country and the best future."
The Lord Chief Justice emphasised to a packed courtroom that the matter was "a pure question of law".
He added: "The court is not concerned with and does not express any view about the merits of leaving the European Union: that is a political issue."
However reacting to the announcement, Nigel Farage feared political classes "do not accept the June 23 referendum result".
He said: "I now fear that every attempt will be made to block or delay the triggering of Article 50. If this is so, they have no idea of the level of public anger they will provoke."