Former Liberal Democrat leader Lord Menzies Campbell said the ruling was a "slap in the face" for Prime Minister Theresa May.

"This is a clear illustration of the well-known legal principle that no matter how high you are, the law is above you," he said.

"It is a slap in the face for the government. It shows the dangers of playing ducks and drakes with the constitution and particularly the sovereignty of Parliament." 

BBC News Channel

Former justice minister and Leave campaigner Dominic Raab says he doesn't think the High Court verdict is going to stop Brexit.

He described the High Court as opening a can of worms and he hopes the Supreme Court will put a lid back on it.

He says the public will take a very dim view of any attempts to frustrate the result of the EU referendum.

A government spokesman said the government "is disappointed" by the High Court’s judgment. 

"The country voted to leave the European Union in a referendum approved by Act of Parliament," he said "And the government is determined to respect the result of the referendum. We will appeal this judgment. "

Image source, Getty Images

A quick recap - Parliament must vote on whether the UK can start the process of leaving the European Union, the High Court has ruled.

This means the government cannot trigger Article 50 of the Lisbon Treaty - beginning formal discussions with the EU - on their own.

Theresa May says the referendum - and existing ministerial powers - mean MPs do not need to vote, but campaigners called this unconstitutional.

The government is appealing.

Read more

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Former education secretary Nicky Morgan described the High Court result as a "very important judgement".

"This is not about stopping Brexit happening or undermining the vote of 23 June, but it's about bringing sovereignty back to Parliament," she told the BBC.

She says the majority of MPs who wanted the UK to remain in the EU, are "mindful" of the way people voted in the referendum.

Robert Bourns, president of the Law Society of England and Wales, "welcomed the opportunity for constitutional clarity which this case brings".

“The question as to whether the decision to trigger Article 50 is one for the government, using the royal prerogative, or for Parliament through statute is central to this court case," he said.

"Most commentators assumed that this case – whatever the outcome in the High Court – would be appealed to the Supreme Court so today’s ruling is a step along the road to a final decision."

House of Commons
Parliament

Labour's shadow Brexit secretary Barry Gardiner says he wants to reject the idea put about from the government front bench that today's High Court ruling "thwarts the referendum result". 

He says that a majority of MPs are committed to leaving, but that "the terms of our leaving must be subject to the scrutiny and consent of this democratically elected House".

International Trade Secretary Liam Fox says there will be "numerous opportunities for the House to examine" Brexit. 

He adds that we'll have to "await the government's appeal to the Supreme Court".

Press Association

Unless overturned on appeal at the Supreme Court, the ruling threatens to plunge the government's plans for Brexit into disarray as the process will have to be subject to full parliamentary control.

Government lawyers had argued that prerogative powers were a legitimate way to give effect "to the will of the people" who voted by a clear majority to leave the European Union in the June referendum.

But the Lord Chief Justice declared:

The government has been given the go-ahead to appeal against the ruling at the Supreme Court but made no immediate announcement about whether it will.

BBC News Channel

BBC News legal correspondent Clive Coleman says the High Court result demonstrates "the executive and the judiciary grinding up against each other".

He says today the "power lies with the judges who say the executive cannot get their way".

Investment manager Gina Miller, who brought the Brexit challenge, said the case was about parliamentary democracy and not about process.

BBC News Channel

House of Commons
Parliament

Conservative Michael Fabricant becomes the first member to ask Liam Fox about a High Court judgement, a few minutes ago. 

He asks Liam Fox if he will join him in "deploring" the High Court's decision that Article 50 must be triggered by Parliament.

Liam Fox says the government is "disappointed" by the ruling and that the "country voted to leave" in a referendum sanctioned by Parliament. 

He says the "government is determined to respect the result" and will "consider it [the judgement] carefully".

BBC News Channel

A statement from one of the claimants outside the Royal Courts of Justice described the result as "a victory for everyone who believes in the supremacy of parliamentary democracy".

Claiming he had voted for Brexit, the campaigner said he did not think parliamentary democracy should be by-passed.

BBC News Channel

BBC Assistant Political Editor Norman Smith says the High Court ruling has thrown an almighty spanner in the works for Prime Minister Theresa May's plans for Brexit.

This means that Parliament will have to give consent to the process of triggering Article 50 for Brexit.

The Government has been given the go-ahead to appeal against the ruling at the Supreme Court.

Parliament must vote on whether the UK can start the process of leaving the European Union, the High Court has ruled. 

This means the government cannot trigger Article 50 of the Lisbon Treaty - beginning formal discussions with the EU - on its own. 

Theresa May says the Brexit referendum and ministerial powers mean MPs do not need to vote, but campaigners argue this is unconstitutional. 

The government is expected to appeal. The prime minister has said she will activate Article 50, formally notifying the EU of the UK's intention to leave, by the end of next March. 

This follows the UK's decision to back Brexit in June's referendum by a margin of 51.9% to 48.1%. The EU's other 27 members have said negotiations about the terms of the UK's exit - due to last two years - cannot begin until Article 50 has been invoked. 

BBC assistant political editor Norman Smith said, if the court's decision is not overturned, there could be "months and months" of parliamentary hurdles ahead.

The government is expected to appeal against the decision, with a further hearing to be held in the Supreme Court.

Read our developing story