My amendment to the motion on the meaningful vote adds the following:
“[N]otes that the Northern Ireland backstop is intended to be temporary; notes that the Vienna Convention on the Law of Treaties makes it absolutely clear that a sovereign state can abrogate any part of a treaty with an international body in case of a fundamental change of circumstances since the Treaty was agreed; notes that making the Northern Ireland backstop permanent would constitute such a fundamental change of circumstances; and therefore calls for an assurance from the Government that, if it becomes clear by the end of 2021 that the European Union will not agree to remove the Northern Ireland backstop, the United Kingdom will treat the indefinite continuation of the backstop as a fundamental change of circumstances and will accordingly give notice on 1 January 2022 to terminate the Withdrawal Treaty so that the United Kingdom of Great Britain and Northern Ireland shall become an independent country once again.”
One of the principles of international law is "pacta sunt servanda" — that agreements or treaties must be binding upon the parties in good faith. It does not, however, follow that treaties cannot be terminated. That they can and have been is also part of international law, though the stated grounds for doing so are limited (and covered in Article 54 onwards of the Vienna Convention).
Treaties of course may be terminated or suspended by specific provision or, even without such, by the mutual agreement of parties. In a given treaty there may also be an intended or implied right to unilateral termination, if a state shows that the parties intended to allow such or if the right to terminate can be implied by the nature of the treaty.
Further grounds are provided when the purposes or object of the treaty have been fulfilled or when it is obvious that the treaty was limited in time or that the mandated period has concluded. If a state violates an important provision of a treaty or agreement another state may legitimately react by terminating the treaty.
The principle of "rebus sic stantibus" means that fundamental changes in circumstance since the conclusion of an agreement mean that a party has legitimate grounds for unilaterally withdrawing from it. This change must have been unforeseen and the effect of such must be to radically transform the obligations entered into by the agreement.
The backstop for Northern Ireland is a worst-case scenario not intended by either party to the draft Withdrawal Agreement to ever enter into effect. Nonetheless, it may do so without being desired by either party. The purpose of my amendment is to provide a helpful reassurance that we will not accidentally end up with an effectively permanent backstop in effect in the event that a transition cannot be agreed. This clarifies the position in international law and reaffirms that the democratically accountable Government’s ability to abrogate the backstop to prevent a semi-permanent customs subservience.