The European Communities Act 1972:
Here is the European Communities Act 1972 (as amended up to 11th August 2016). It is - "An Act to make provision in connection with the enlargement of the European Communities to include the United Kingdom, together with (for certain purposes) the Channel Islands, the Isle of Man and Gibraltar."
The ECA as originally enacted has been amended as necessary over the years and the modern European Union has developed - Timeline of the EU.
Events leading to the ECA 1972
The UK applied to join the European Economic Communities in 1967 and negotiations eventually began in October 1970. The question of whether Britain should sign the Treaty of Accession was debated in the House of Commons in October 1971. Domestic opinion was strongly against membership and there was considerable concern over whether the terms negotiated were good enough for Britain. Doubts over many issues affecting Britain's future were aired in a debate that lasted six days. Hansard for 28th October 1971 records that the House of Commons approved the following motion by 356 votes to 244.
"That this House approves Her Majesty's Government's decision of principle to join the European Communities on the basis of the arrangements which have been negotiated."
Prime Minister Edward Heath signed the Treaty of Rome on 22nd January 1972 - Parliament Treaty of Rome.
The signing of the Treaty of Rome did not have any immediate effect in the domestic legal systems of the UK because the UK has a dualist system with respect to Treaties. This system requires Parliament to enact legislation in order to give legal effect in domestic law to a treaty. A Bill, consisting of just 12 clauses, was introduced into Parliament. Some 300 hours of debate followed before it became law as the European Communities Act 1972. There was no referendum even though it was known that public opinion was, generally, either hostile or uncertain. See BBC - A short history of UK referendums.
Note: Following the "LEAVE" vote in the 2016 European Union Referendum, there has not (as yet) been any extensive debate in Parliament let alone approval of any decision to leave.*
The EU Treaties:
The Treaties constitute the fundamental law of the EU.
- Treaty on European union (Consolidated version 2016) - TEU
- Treaty on the Functioning of the European Union (Consolidated version 2016)- TFEU
The general implementation of the EU Treaties is the purpose of section 2 of the European Communities Act 1972. (The phrase EU Treaties is defined in the ECA 1972 section 1 - as amended).
The Treaties empower the EU to make REGULATIONS. A Regulation has general application and is binding in its entirety and directly applicable in all Member States. The words "directly applicable" mean that a regulation has legal effect in Member States without any further need for national legislation. The ECA 1972 section 2(1) provides for such directly applicable EU law.
A further form of EU legislation is the DIRECTIVE. A directive is binding, as to the result to be achieved, upon each Member State to which it is addressed, but it is left to national authorities to choose the form and method of implementation. The ECA 1972 section 2(2) contains a power for the making of national legislation or the purpose of implementing any EU obligation of the United Kingdom etc.
Implemented in national law by statutory instrument 2012 No. 3113
(The word "Regulations" here refers to a UK form of Statutory Instrument and not to a Regulation of the EU).
The central importance of the ECA 1972 is clear since, without this Act, neither the EU Treaties nor other EU legislation would have effect in the domestic legal systems of the United Kingdom.
Brexit - A complex problem:
In the 43 years and 8 months since 1st January 1973, the ECA 1972 has enabled a mass of EU-related legislation to take effect in domestic law. One consequence of Brexit is that ALL of this legislation will eventually need to be identified but, with appropriate resources, that ought not to be beyond the wit of government lawyers though there can be no doubting the difficulty!
Having identified the legislation it will be necessary to decide, for each item of this legislation, whether it can be abandoned or whether it offers something of value to the UK that ought to be retained in domestic law. Some of those decisions will depend on whatever the on-going UK-EU relationship is to be and that will not be fully known until the conclusion of the negotiations which will commence in earnest when the UK gives notice (under Article 50) of a decision to leave.
As to what may be retained, the political climate at Westminster is also likely to play a significant part. Some decisions will be politically controversial such as whether workplace rights will be retained where such rights have their origins in EU law. On this see University of Bristol - Worker's Rights- Opinion of Michael Ford QC.
All of this points to a lengthy and difficult process eventually leading to Brexit. The difficulties - both legal and political - should not be underestimated. There is a mountain to climb before the ECA 1972 can be repealed.
* The Independent - 28th August - Theresa May 'acting like Tudor monarch' over plans to deny parliament Brexit vote