International Law backs self-determination.


With growing lack of confidence in the EU across Europe and rising pressure for a UK referendum on membership, people are asking what would happen if the UK tried to leave the EU?



Treaty law is part of International Law. It is a complex subject, and not an exact science, and has several working rules that need to be balanced against each other.

All 27 EU member states are members of the United Nations, signing its 1945 Charter before joining the EU. The Charter holds

"In the event of a conflict between the obligation between Members of the United Nations under the present Charter and their obligations under any other international agreement, their obligations under the present Charter shall prevail" (Article 103).

The Treaty of Rome (ToR), 1957, to which the UK acceded in 1973 held:

"The rights and obligations arising from agreements concluded before the entry into force of this Treaty between one or more Member States on the one hand, and one or more third countries on the other, shall not be affected by the provisions of this Treaty". (ToR Art.234, then the Treaty of Nice, then the latter's direct successor, the Treaty of Lisbon (ToL), ref. TFEU Art. 351)

That is explicit. So is the UN Charter's respect for the principles of "sovereign equality for all its members" and "self determination of peoples" (Arts. 2.1 and 1.2). The Universal Covenant on Civil and Political Rights, 1966, also upheld the right of nations to self-determination. This came into force in 1976.

In addition, the Charter holds that "All members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state..." (Art.2.4).

If the UK wished to leave the EU, then the EU could not stop it.



The Treaty of Lisbon has its own rules for co-ordinated withdrawal. These typically specify a two-year run-down of membership although a different date can be agreed. (ref. ToL TEU Title VI, Art. 50).

Member States undertake not to "submit a dispute concerning the interpretation of the Treaty to any method of settlement other than those provided for therein". (ToL TFEU Art.344).

The EU's 'supreme court' is the Court of Justice of the European Union. Also known as the 'European Court of Justice' or ECJ, it has a remit to interpret EU membership Treaties (ToL TEU Title III Art. 13, TFEU Arts. 251 et seq.).

However, like other EU institutions, it "shall act within the limit of the powers conferred on it by this Treaty" (ToL TEU Title I, Art.5). The ECJ can rule within the EU context, but must interpret membership obligations within this constraint.



The above judgements apply to those countries that have legally concluded membership of the EU. Research has shown that this is debatable in the case of the UK.

To enter into force, the membership Treaty "shall be ratified according to respective constitutional requirements". (ToL TFEU Art.357). There is evidence elsewhere that the UK's ratification was contrary to established constitutional requirements, and that UK legal judgements upholding it are contradictory, and therefore flawed.

In the event of a rigorous judicial review or summary appeal, a legal ruling holding that EU membership is null and void is a foreseeable possibility. As with King Henry VIII's first marriage in the 16th century, the issue would seem to be not 'divorce' but 'annulment'.



In 1969, the UK signed the Vienna Convention, which officially came into force in 1980 on gaining a quorum of signatures. As at 18.2.13, only the following EU members were not signatories: France, Rumania.

However the Convention is International Law, used at the UN for the interpretation of Treaties, and there is no reason for thinking that the two named countries would not accept it.

According to the very informative and readable The International Law of Treaties website, seen in 2004, the Convention is, in practice, applied to Treaties concluded before 1980, as it incorporated customary rules in force before then. The Convention is therefore used as a lens for interpreting the scenario whereby the UK chose to withdraw from the EU.

The Convention supports the principles of "self determination of peoples... sovereign equality and independence of all States... non-interference in the domestic affairs of States".

Termination of a Treaty

Generally Treaties should be terminated unanimously (Art.54) but it holds that invalid Treaties can be 'denounced' or 'withdrawn from' (Art.42).

Grounds for invalidation can include:

The Treaty of Lisbon was only passed after the coercion of the Irish people who had rejected it in a free vote in 2008.

It is also noted that although generally a later Treaty over-rides the relevant parts of an earlier Treaty (Art.30), Article 103 of the UN Charter, which upholds national sovereignty, is preserved.

Winding-down and Arbitration procedures

The current EU membership Treaty [Lisbon] has provision for termination within 2 years or as agreed, and the customary twelve months notice of termination (under VC Art.56) would not be absolutely necessary.

A party wishing to terminate a Treaty must notify the other parties, with reasons. Normally they would need to give at least three months' notice, but can simply terminate in cases of "special urgency" (Art.65).

If any other party to the Treaty objects, they can seek a solution via Article 33 of the Charter of the UN. However, given the legal perspective outlined, it is inconceivable that the UN or its International Court of Justice could rule against explicit fundamentals in its Charter.

In the unlikely event of escalation, the UN would be tasked with trying to reach an amicable settlement (Annex to Convention).

Ongoing relationships

If a Treaty is legally terminated, it releases the parties from any obligation to further work to ("perform") the Treaty. However it does not affect any "right, obligation or legal situation" arising from the Treaty (Art. 70).

This implies that a complex set of trading and political co-operation relationships would need to be reviewed - including a mechanism for the reconciliation of any differences in understanding.

An invalid Treaty is void and has no legal force (Art.69). However 'acts performed in good faith' before the Treaty was invalidated are not made unlawful solely by its invalidation, and the parties involve may require the position concerning their relationship to be established.

This implies that the UK would need to confirm the continuation of any 'intergovernmental agreements' made with other EU Member States, and the nature of its relationship to them through international bodies such as the World Trade Organisation and NATO.

Other obligations existing under International Law are unaffected (Art. 43).

Appendix: Could the UK be thrown out of the EU?

The Treaty of Lisbon has a mechanism whereby the EU can discipline a Member State for a 'serious and persistent breach' of Treaty values (ToL, TEU Title I, Art.7). These are loosely defined but include "the rule of law" and providing the EU with the means necessary to attain its objectives and carry out its tasks (ToL, TEU Title I, Arts.2, 3 & 4).

The offending Member State can have its 'rights' suspended, but its 'obligations' would continue. The ECJ can levy penalties such as unlimited fines for a technical Treaty infringement.

If say, Sweden, which has no single currency opt-out, stated that they rejected a single currency outright, this would effectively challenge the EU's fundamental principles.

Alternatively, a maverick Member State might continually block further integration (such as on fiscal integration/stability, EU defence initiatives requiring unanimity or even an increase in the EU budget). This might cause the Member States supporting further integration to regard the maverick as no longer fully subscribing to the political ends of the European Union.

They might find it politically more credible to threaten to terminate the current Treaty with the maverick, as acceptance of Treaty objectives is a condition of membership (ToL, TEU Title I, Art.5).

The Convention covers a 'material breach of a multilateral Treaty' (Art.60). The other Member States can either terminate the current Treaty with the maverick, or between all parties.


Footnotes: This article is provided as a discussion document in the cause of democratic debate.
For simplicity, the terms EEC, EC and EU are used interchangeably.
The latter two overlap and are subtly different, however all legislation is technically 'EU Law'.
Before 1987 'EC' was used to mean the three 'European Communities' (Economic, Atomic Energy, Coal & Steel) then was known as a consolidated 'European Community'.


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This page compiled: 26 June 2004, updated: 19 Feb 2013