The circumstances surrounding the EU referendum are so bizarre, so chaotic and so impassioned that it is easy to overlook the fact that the UK’s withdrawal from the union would simply consist of two administrative acts performed by the government, acts that are subject to well-settled forms of legal analysis and legal evaluation. The government decides that the UK will withdraw from the EU; and the government notifies the European council of that intention.

There is strong reason to believe that the government’s withdrawal decision would be unlawful, and hence that the notification would be invalid.

The government acts in question are, as a matter of legal analysis, the exercise of legal powers. It is of the essence of legal powers that they have limits. The reason is that the exercise of a legal power alters the legal situation of anyone to whom that exercise applies. It may reduce their legal freedom, deprive them of rights, and impose new legal obligations. A legal power of a public authority, such as the government, may affect the legal situation of very many people. For this reason, the courts are particularly firm in keeping public authorities within the limits of their powers. UK withdrawal from the EU would affect the legal situation of every person in the UK, and the legal situation of many other people elsewhere.

Parliament voted to hold the EU referendum – it can vote to ignore it | Robert Hunter Read more

At the request of a person directly affected by the exercise of a power, a court may conduct a so-called judicial review to determine whether the exercise of a public power on a given occasion is, or is not, within the limits of the power. This applies to all public powers at all levels of government and administration.

This activity of the courts is a product of centuries of constitutional struggle to control the temptation to absolutism of kings and, now, of the executive branch of government. The principle of the rule of law has become a fundamental principle of our constitution and of liberal democracy in general. All public power is subject to the law applied and enforced by the regular courts. Until 2015, the lord chancellor, as head of the judiciary, was the ultimate guardian of the rule of law. Then a lord chancellor was appointed who was not a judge but a government minister.

As the powers of public authorities have increased massively in volume over the last hundred years, the law of judicial review has developed to a corresponding extent. There are thousands of decided cases and whole libraries of commentaries. As a branch of law it is dense and subtle and controversial – especially when it involves undoing the work of an elected body; and controversial within a never-ending debate about how vigorous the courts should be.

So that they are not themselves seen as arbitrary, the courts are constantly developing and refining general principles of judicial review. In the light of the current state of those principles, two elements of the government’s decision-making in relation to withdrawal from the EU seem to be worthy of judicial review.

First, the original motivation for the holding of a referendum seems not to have been the public interest, but the particular interest of a political party. Especially in cases relating to local authorities, the allegation of a corrupt abuse of a public power is familiar – for example, a planning decision favouring a friend of the chairman of the planning committee. It would be bold to extrapolate such a case to the level of national government. But it is worth noting that it would be a challenge not to the Referendum Act of Parliament – challenging the validity of an act of parliament would raise formidable problems of general constitutional law – but to the actions of the government in the process leading up to that legislation.

Secondly, the courts, in countless cases, have entered into consideration of the substance of public decisions. They do not aim to second-guess the policy embodied in the decision. But they can take the view that the very substance of the decision is flawed in some fundamental way that takes it beyond the outer limits of the power. They have devoted much effort to finding general formulas for justifying this extreme step, reflecting again their crucial concern that they themselves must not seem to be acting arbitrarily.

Don’t mourn, organise: a seven-step plan for fighting back against the Brexit vote | Kat Craig Read more

In the light of the current law, it is possible that a court might take the view that it is arbitrary and unreasonable and disproportionate, in the legal sense of those words, to base the vastly important decision to withdraw from the EU on the opinion expressed by a bare majority of people taking part in a referendum provided for in an act of parliament – but an act of parliament that makes no provision for the legal effect of that referendum – thereby ignoring the opinion expressed by a very large minority. Governments are governments of the whole nation, not of a favourable constituency.

In the matter of withdrawal from membership of the EU, the government is not acting under its “prerogative power” in the field of foreign relations – an inherited power of the crown that needs no legislative basis. It is using the powers contained in article 50 of the treaty on European Union, which is part of UK law through the European Communities Act 1972. Article 50 explicitly leaves the legality of a withdrawal decision to national law. An unlawful decision under UK law would be invalid for the purposes of article 50.

The legality of the proposed government acts is open to serious question, a question that can only be finally answered in the courts.