The landmark High Court decision handed down on 3 November has been widely reported and commented on. The Court held that the Government does not have the power under royal prerogative to trigger Article 50 of the Lisbon Treaty (Article 50) and that Parliament alone has this power and must therefore be consulted in this process. 

The Supreme Court announced last week that the Government's appeal will be granted and a date has been set for the Supreme Court hearing in the week commencing 5 December 2016, with a decision expected in early January. Such is the gravity of this fundamental constitutional issue that for the first time in its history the Supreme Court will sit with a panel of all 11 of its permanent Justices.

To complicate matters even further, the Belfast High Court was seized in parallel proceeding raising similar arguments under the 1998 Good Friday peace agreement. It ruled less than a week before the decision of the English High Court that there is nothing in the Good Friday agreement that prevents the Government from triggering Article 50 without first consulting the Northern Ireland Assembly or Parliament. The Irish decision has also been appealed.

Claimants

The identity of the lead Claimant, an investment manager called Gina Miller, has been well publicised. Submissions were also made on behalf of a diverse range of individuals including nationals from England, Ireland, Scotland, Wales and Gibraltar and a Canadian citizen whose right to reside in France derives from her Husband's British citizenship.

The Scottish and Welsh governments had watching briefs and so they were attending the proceedings as observers only.

Legal issue

Put plainly, the UK Parliament is sovereign and, in theory, this means that there is no limit on what it can achieve through legislation. Senior Government ministers are able to perform certain actions, without parliamentary authority to do so, using their prerogative powers. Prerogative powers are specific powers which were originally held by the Monarch but are now generally exercised by senior Government ministers. One example is the power to negotiate international treaties on behalf of the UK.

The European Union Referendum Act 2015 (Referendum Act), which gave the government power to call the Referendum on 23 June, did not specify what should happen following the referendum. Critically, the Referendum Act did not state that the result of the referendum would be binding on Parliament.

The legal question before the court hinged on the wording of Article 50, which allows Member States to decide to withdraw from the European Union "in accordance" with their own "constitutional requirements". Thus, the question that arose was whether this necessitated an Act of Parliament or whether the Government held prerogative powers to do the same.

The Claimants' arguments

The argument central to the Claimant's case was as follows:

• Once notification has been given under Article 50, it cannot be revoked.
• The inevitable consequence of notification under Article 50 is that rights granted by Acts of Parliament (including rights granted pursuant to the European Communities Act 1972 (the ECA) which incorporated EU law into domestic law) will be lost.
• Since Parliament is sovereign, the Government cannot use its prerogative powers to defeat rights granted by Parliament – an Act of Parliament is needed to take such rights away.

The Claimants identified three categories of rights which they stated would be lost following notification under Article 50:

• Rights which Parliament can replace or replicate, e.g. employment law rights.
• Rights which Parliament can replace depending on any deal with the EU following withdrawal negotiations, e.g. the right to work in another EU state.
• Rights which will be lost and cannot be replaced by Parliament, e.g. the right to vote in an EU parliamentary election and the right to refer a case to the ECJ.

The Claimants also argued that the Referendum Act did not give the Government authority to trigger Article 50 since there is nothing in the Act which empowers someone other than Parliament to take that course of action.

The Decision

The judges Lord Chief Justice Lord Thomas, Master of the Rolls Sir Terence Etherton and Lord Justice Sales (Judges) took care to deal simply with the question of law, rather than give an opinion on the "political wisdom or otherwise of the withdrawal by this county from the EU”.

The Judges gave the following reasons for their decision:

• The Referendum Act did not, nor did any other Act of Parliament confer statutory authority on the Government to give notice under Article 50.
• There is nothing in the text of the ECA that Parliament intended when it enacted the Act, that the Crown would retain its prerogative power to withdraw from the EU treaties.
• The stronger the constitutional principle, the stronger the presumption that Parliament did not intend to override an Act, and the stronger the material required, in terms of express language before any inference can be drawn.
• Article 50 will inevitably lead to the withdrawal from the EU and therefore, loss of domestic rights which have been given by an Act of Parliament. It is contrary to the constitutional principles of the sovereignty of Parliament for the Crown to change domestic law by the exercise of prerogative powers.

The counter arguments

The Government failed to persuasively convince the Judges that it can rely on prerogative powers to initiate the process of leaving the EU. Its case before the High Court can be summarised as follows:

• The Government has a prerogative power to enter into and withdraw from international treaties.
• Prerogative powers can only be restricted by clear statutory wording.
• Parliament had not circumscribed the use of the relevant prerogative power to trigger Article 50.
• Had Parliament intended to restrict the use of these powers, it should have made this clear in the Referendum Act.

The Government also argued that the Claimants had overstated the rights lost to individuals and that some of the rights claimed to have been incorporated into domestic law by the ECA are actually rights granted by the EU treaties. (For example, if a UK citizen wishes to reside in France, this is a right granted by an EU treaty and French domestic immigration law.)

The Government did concede that an Article 50 Notification could not be conditional nor could it be revoked. However, it has been reported this week that the Government may well change tack on this line of argument before the Supreme Court as it has been consulting constitutional law experts to say that Article 50 could be reversed at any time by Parliament.

The government also noted that it was likely that any agreement between the UK and the EU as regards the terms of the UK's exit would, in effect, have to be approved by the House of Commons. The House of Commons can delay ratification of an international treaty by passing a resolution that the treaty should not be ratified. However, this is not the same as a full Parliamentary debate to pass new law.

Looking to the future

Practically, the High Court's decision simply means more watching and waiting, but it is clear that it is not intended to be a reversal of the referendum result. If the High Court's decision is upheld by the Supreme Court, it may well not alter the course of Brexit but it could delay the eventual triggering of Article 50.