With growing lack of confidence in the EU across Europe and the possibility of the EU Constitution being rejected in a UK referendum, people are asking what would happen if the UK tried to leave the EU?

At a press conference to convince France of the merits of the expanded EU, M Chirac referred to proposals aired in Brussels and Berlin that would require member nations to ratify the constitution or leave the EU. This could be a "positive solution", M Chirac said. "I am not against the idea of using methods of friendly pressure with countries that are refusing the constitution because that blocks all the others." (Times, 30.4.04)

On 20.6.04, Tony Blair was quoted by EUbusiness as rejecting a re-run of a referendum to ratify the Constitution. EUbusiness added that unanimity would be needed, both to conclude a new (Constitutional) Treaty and to end an existing one.



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 25 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" (Art 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, now Treaty of Nice (ToN), Art 307)

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.



Some individuals have claimed that the Treaties for EU membership do not contain any provision for withdrawal. However, when the Danish dependent territory, Greenland, wished to leave the EU in 1985, the Member States simply amended their Treaty to allow this to happen. This is in spite of the observation that the then-current Treaty had no explicit clause for withdrawal.

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". (ToR Art 219, ToN Art 292).

The EU's 'supreme court', the European Court of Justice (ECJ) has a remit to interpret EU membership Treaties (ToR Arts 177 & 164, ToN Arts 220, 239).

However, like other EU institutions, it "shall act within the limit of the powers conferred on it by this Treaty" (ToR Art 4, also ToN Art 5). The ECJ can rule within the EU context, but must interpret membership obligations within this constraint.

According to a newspaper report (details being confirmed) in Spring 2004, UK courts struck down an ECJ ruling that was beyond the scope of the latter's powers. The national legal order is further recognised, as under some circumstances, disputes to which the EU is party can be under the jurisdiction of Member States (ToR Art 183, ToN Art 240).

Finally, the international legal framework was recognised in an original text on trade restrictions: "The obligations on Member States shall be binding only in so far as they are compatible with existing international arrangements" (ToR, Art 37.5).



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". (ToR 247, Ton Art 313). 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 29.6.01, the following EU members were not signatories: France, Rep. Ireland, Portugal, Luxembourg; also Malta.

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

According to the very informative and readable The International Law of Treaties website, 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:

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

Given the precedent of Greenland, it could not realistically be claimed that the current EU membership Treaty has 'no provision for termination', and twelve months notice of termination (under Art 56) would not be 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 Nice has a mechanism whereby the EU can discipline a Member State for a 'serious and persistent breach' of Treaty principles (ToN, 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 through with its policies" (ToN, Art 6).

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, or the UK, which has a leaky and basically temporary 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 the proposed European Constitution, 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 (ToN, Art 10).

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 (for instance to enable a Constitutional Treaty to come into force).


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 'EC'.
Before 1987 'EC' was used to mean the three 'European Communities' (Economic, Atomic Energy, Coal & Steel) then was known as a consolidated 'European Community'.


|For a view on the legality
of the UK's EU membership

|[Legacy] EU legal order in detail|

|[Legacy] EU legal order made simple|

|What if the Constitution isn't
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This page compiled: 7 July 2004, link/title updated: 3 May 2012