18/04/2013 10:02 BST | Updated 18/06/2013 06:12 BST

Would the Law Change if the UK Was to Leave the EU?

At present EU law is supreme to UK law and this is a major sticking point for many Eurosceptics and is often used as an argument for the UK's exit from the EU. But what would the legal implications of the UK's exit from the EU actually be? Would EU law be completely rejected in favour of national law?

Unfortunately the answer is not that simple - and not one that is likely to be welcomed by the Eurosceptics. EU law is now firmly imbedded in legislation and case law and would not be easy to unravel.

EU law is supreme to the law here in the UK through the European Communities Act 1972 (ECA), and this is what gives EU law legal effect in the UK. The traditional view is that if the ECA was repealed by Parliament then EU law would no longer be supreme. However, rejecting EU law would not be that straight forward.

The UK has established the principle of supremacy in case law by giving EU law priority, to the extent of altering the meaning of UK law to make it compatible with EU law.

The EU has also established the principle of supremacy in case law by confirming the EU as an independent legal order supreme to old and new national law, even national constitutions, and that if there is a conflict between national law and directly effective EU law, EU law prevails and national law can be ignored. In fact, governments will be liable for financial loss suffered as a result of their breaching EU law.

But would EU law still be supreme if the UK were to repeal the ECA? Judges have argued that if Parliament were to repeal the ECA, then our courts must give effect to Parliament's wishes and EU law would no longer be supreme. This is unlikely as long as we remain members of the EU, but it is possible, and the assumption would suggest that the process would be fairly clear cut and UK Parliamentary Sovereignty seems to remain intact.

However, some leading judges in the UK have said that Parliamentary Sovereignty is no longer absolute, and that as they created the doctrine - they can therefore amend it, i.e. the Rule of Law is there to control Parliament's legislative sovereignty and can work as a check and balance upon Parliament's legislative power. If Parliament tried to legislate contrary to the Rule of Law then the courts, according to the UK Constitution, could prevent them from doing so. If judges see EU law as part of the UK's Rule of Law, they could prevent Parliament from repealing it.

Here in the UK, Judges have already altered the principle of Parliamentary Sovereignty by removing the doctrine of implied repeal (which means a later act of Parliament repeals earlier acts of Parliament that are inconsistent with the later act), to the ECA. They ruled the ECA could not be impliedly repealed because it is a constitutional act and only a later constitutional act could repeal it. This in turn raised the argument that as a result of the ECA, EU law is now entrenched into UK law and is unrepealable. However, the court rejected this argument because Parliament cannot bind its successors by stipulating against repeal of the ECA.

The constitutional Act reasoning attempts to explain why implied repeal does not apply to the ECA, but it's not clear whether higher courts would adopt it. The courts could decide that it is the wording of the ECA itself which has the effect of preventing implied repeal and thus EU law has become entrenched into UK law.

EU and national law have developed EU supremacy beyond nations' individual political aims and legislation. It could be said that the ECA merely allowed for EU law to become entrenched in UK law and there is no going back. Judges could adapt the doctrine of Parliamentary Sovereignty and give way to EU supremacy if we leave the EU. If the supremacy of EU law is a part of our UK Rule of Law, then judges must uphold the Rule of Law.

If we were ever to leave the EU or repeal the ECA, the outcome is not as clear cut as many would hope. Repeal and withdrawal from the EU will not necessarily mean judges will not uphold EU law, which will come as a surprise to those Eurosceptics among us.