The UK Government has been defeated in the landmark Brexit High Court challenge over whether Article 50 can lawfully be triggered without a vote by Parliament.

Lord Chief Justice Lord Thomas handed down the decision in the Royal Courts of Justice this morning.

His verdict read: “The court does not accept the argument put forward by the Government. There is nothing in the text of the 1972 Act to support it.

“In the judgment of the court the argument is contrary both to the language used by Parliament in the 1972 Act and to the fundamental constitutional principles of the sovereignty of Parliament and the absence of any entitlement on the part of the Crown to change domestic law by the exercise of its prerogative powers. The court expressly accepts the principal argument of the claimants.

“For the reasons set out in the judgment, we decide that the Government does not have power under the Crown’s prerogative to give notice pursuant to Article 50 for the UK to withdraw from the European Union.”

The Government will appeal the decision, with the appeal heading straight to the Supreme Court in early December. The case is understood to have been fast tracked following Prime Minister Theresa May’s pledge to trigger Britain’s exit from the EU next spring.

Successful claimants were represented by Mishcon de Reya, Bindmans and Edwin Coe. Leading the charge was Blackstone Chambers’ Lord Pannick QC as well as Matrix Chambers’ Helen Mountfield QC and Rhodri Thompson QC.

Representing the UK Government, the Attorney General instructed Blackstone’s James Eadie QC and 11KBW’s Jason Coppel QC.

Bindmans partner Halford, who represented the People’s Challenge group in the claim, said in a statement: “The oversight, control and democratic accountability needed for decisions on Brexit have to match the consequences of those decisions for UK citizens. That is why our constitution empowers Parliament, not the government, to take these decisions.

“The People’s Challenge group and thousands of backers unhesitatingly committed to defending Parliament’s sovereignty. They have prevailed so far and will resist the anticipated government appeal in the Supreme Court.”

The Law Society has also been swift to respond to the groundbreaking verdict. President of the Law Society of England and Wales Robert Bourns said: “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. 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.”

Meanwhile a Clifford Chance partner said today’s decision heralds further uncertainty for the business world. The firm’s co-chair of public policy Simon Gleeson said: “This is just round one. Whether this tussle continues solely in the courts or also Parliament, in the form of a bill, it will continue to extend uncertainty and make planning and investment tougher for businesses.”

The legal line-up

For the first claimant, Gina Miller

Blackstone Chambers’ Lord Pannick QC and Tom Hickman, Matrix Chambers’ Rhodri Thompson QC, and Monckon Chambers’ Anneli Howard, instructed by Mishcon de Reya partner Rob Murray

For the second claimant, Deir Tozetti Dos Santos

Maitland Chambers’ Dominic Chambers QC and Benjamin John, and Matrix Chambers’ Jessica Simor QC, instructed by Edwin Coe

For the defendant, the Secretary of State for Exiting the European Union

Blackstone Chambers’ James Eadie QC, and 11KBW’s Jason Coppel QC, Tom Cross and Christopher Knight, instructed by the Attorney General

For the first interested party, the People’s Challenge

Matrix Chambers’ Helen Mountfield QC, Monckton Chambers’ Gerry Facenna QC and Jack Williams, and Brick Court Chambers’ Tim Johnson, instructed by Bindmans partner John Halford

For the second interested party, AB, KK, PR and Children

No 5 Chambers’ Manjit Gill QC and Ramby de Mello, and 43 Temple Row Chambers’ Tony Muman

For the interveners, George Birnie and ors

Henderson Chambers’ Patrick Green QC, Henry Warwick, Paul Skinner and Matthieu Gregoire

And on Twitter…

The politicians

The lawyers

The journalists