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Could the Withdrawal Agreement be terminated under international law?

Published Friday, December 21, 2018

Could the UK unilaterally terminate the Withdrawal Agreement under international law if the Irish backstop, which the Agreement says is intended to be temporary, became permanent? An amendment from Sir Edward Leigh to the Government’s motion on approving the Withdrawal Agreement called for an assurance from the Government that it would terminate the Withdrawal Agreement if the EU refused to agree to removing the backstop at the end of 2021. This note looks at provisions in the Vienna Convention on the Law of Treaties for terminating and denouncing treaties and arguments about whether these might apply in this particular case.

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The Leigh amendment

An amendment from Sir Edward Leigh to the Government’s motion on approving the Withdrawal Agreement called for an assurance from the Government that it will terminate the Withdrawal Agreement if the EU refused to agree to removing the backstop at the end of 2021.

The Vienna Convention on the Law of Treaties

But could the UK terminate the Withdrawal Agreement under provisions in the Vienna Convention on the Law of Treaties (VCLT)? The VCLT sets out limited circumstances in which a treaty can be denounced when it lacks relevant clauses on denunciation and when the parties to the treaty cannot be brought into agreement. These circumstances include cases where:

  • the parties clearly intended to admit the possibility of denunciation, or a right of denunciation is implied by the nature of the treaty;
  • a further treaty covering the same subject matter is concluded by all the parties to the existing treaty and supersedes this treaty, or the two are incompatible;
  • there is a material breach of a bilateral treaty by one party, or in certain circumstances by a party to a multilateral treaty;
  • it is impossible for a party to observe a treaty because of an essential treaty objective disappearing;
  • there has been a fundamental change in the circumstances under which the parties originally concluded the treaty, and that change in circumstances has not resulted from the actions of the state wishing to denounce;
  • a new peremptory norm of general international law has emerged with which the treaty conflicts.Strictly speaking, the Leigh amendment does not claim that the Vienna Convention applies, but it implies that it does. At the very least, the Vienna Convention is a very strong guide to the international law rules - and it works as a guide even for the EU (which is not a party to it), as confirmed by the CJEU in its Wightman judgment on 10 December 2018.

Does the Vienna Convention apply?

The Withdrawal Agreement is a treaty between the UK (a state) and the EU (an international organisation), whereas ‘treaty’ is defined in the VCLT as an agreement between states; and the Vienna Convention involving international organisations is not yet in force. 

Strictly speaking, the Leigh amendment does not claim that the Vienna Convention applies, but it implies that it does. At the very least, the Vienna Convention is a very strong guide to the international law rules - and it works as a guide even for the EU (which is not a party to it), as confirmed by the Court of Justice of the EU (CJEU) in its Wightman judgment on 10 December 2018.

'Material breach' and 'fundamental change of circumstances'

Some commentators have suggested that either the ‘material breach’ (Article 60) or ‘fundamental change of circumstances’ (Article 62) provisions in the VCLT might allow the UK to unilaterally denounce or terminate the agreement if the Irish backstop were to become permanent. But there are difficulties with these suggestions. Proving a ‘material breach’ of “best endeavours” would be extremely difficult; and crucially, a continuation of the backstop would not be a fundamental change of circumstances within the meaning of the VCLT.

Dispute resolution in the Withdrawal Agreement

However much international law applies, any dispute about the Withdrawal Agreement will have to be settled within the Withdrawal Agreement dispute settlement mechanisms or by subsequent international agreements between the parties to it.

Commons Briefing papers CBP-8463

Authors: Vaughne Miller; Sylvia de Mars

Topics: EU law and treaties, International law, International organisations, International politics and government, United Nations

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