In 1972, the British Parliament adopted the European Communities Act (ECA), which approved its compliance to the European Union and validated at the same time all European legal standards in British law. A few years later, Judges recognised both the primacy of European law and its direct effect in the British legal system through the cases Factortame (1991)  and Equal Opportunities Commission (1992) . The ECA established an unprecedented relationship between the British and European legal order by recognising in advance the validity of all regulations adopted at the European level without the need for further transcription by the national parliament.
In its white paper from March 31st, the Government gives its road map to avoid creating a legal vacuum after Brexit. Indeed, according to the Government, no less than 12,000 European regulations have direct effect in British law, however other sources mention more than 20,000 pieces of legislation. European law now governs entire sections of the society in the UK, particularly in the sectors of industry, services, environment, agriculture, transport and in other fields such as health or employment law. How to ensure continuity after Brexit? Mostly, how to avoid legal uncertainty?
Converting the body of European Legislation into UK law
The Government has announced it will adopt a Great Repeal Act that will integrate the entire corpus of European law (the so called “acquis”) into UK law once Brexit becomes effective. The jurisdiction of the EUCJ will no longer apply: the European Court will not have any future role in the UK after Brexit although national courts will still be able to refer to its past jurisprudence to interpret provisions forming part of the European body of law. Furthermore, the Great Repeal Act will give the government the power to adopt regulatory acts with the force of law to amend the provisions of European law contrary to the principles of Brexit.
As a result of its integration into the European Union, the UK has evolved its Constitution to admit the direct effect and the primacy of European law. A constitutional revolution that challenged the principle of parliamentary sovereignty, as stated by the great jurist Dicey, to admit the principle that parliament could bind its successors. This revision was sanctified in the Thoburn case (2002) , in which the the idea of “constitutional statutes” was conceived, other examples being the Bill of Rights and the Human Rights Act now regarded as higher than ordinary laws in the legal hierarchy.
The biggest historical legal issue
European law, which entered by the back door through a simple Act of Parliament, has slowly overturned the British legal order. This is in line with the constitutionalisation movement that all countries have experienced over the same period. It was a genuine “incoming tide” , as related by Denning, which changed the constitution of the UK. Today, the United Kingdom faces its biggest legal challenge as the European tide falls.
The pragmatic approach taken by the current Government seems to be the sensible solution and will, hopefully, minimize uncertainty and guarantee the UK’s legal security.
 CA, March 22,1989, R. v Secretary of State for Transport Ex p. Factortame Ltd, 2 C.M.L.R. 353
 QB, October 10, 1991, R. v Secretary of State for Employment Ex p. Equal Opportunities Commission, 1 All E.R. 545
 QB division, February 18, 2002, Thoburn v. Sunderland City Council, 3 W.L.R. 247
 CA, May 22, 1974, HP Bulmer Lt v. Bollinger S.A, 1 Ch. 401