Richard Ekins is Head of Policy Exchange’s Judicial Power Project and Associate Professor in the University of Oxford, Fellow of St John’s College.  Sir Stephen Laws was formerly First Parliamentary Counsel.  Guglielmo Verdirame is Professor of International Law at King’s College London and practises at 20 Essex Street Chambers.

For many MPs, the main concern with the Withdrawal Agreement is the feasibility of the UK exiting from the backstop, i.e. the Protocol on Ireland/Northern Ireland to the Withdrawal Agreement. The backstop is expressly “intended to apply only temporarily”. However, in its current form, the Protocol makes no provision for a right of unilateral withdrawal, even though this right is not uncommon in treaties (Article 50 of the Lisbon Treaty is an obvious example).

Yesterday the Attorney General, in his role as legal adviser to the Commons, advised that the absence of a right of unilateral withdrawal did create a “legal” risk that the UK might find itself having to remain in the backstop indefinitely. He argued powerfully that the risk was nevertheless worth taking, and low, both because of political factors and for legal reasons. The political factors centred principally on the likely discomfort from the EU side – if the backstop continued indefinitely – at the benefits it confers on the UK in return for limited burdens. The legal reason related to the legal uncertainty that would arise under EU law if the backstop continued indefinitely because, having been entered into under Art 50, it could not lawfully be the basis of a permanent relationship. It is not yet clear to what extent these arguments have changed minds.

While Parliament is not able to enact a unilateral right to withdraw from the backstop – the right would have to arise under international law – Parliament might be able to secure some strengthening of the UK’s position about the termination of the backstop and thus help mitigate the legal risk explained by the Attorney General.  In a new paper for Policy Exchange, published yesterday while the Attorney General was speaking, we outlined the legal position as it stands, explaining how Parliament and Government jointly could mitigate the legal risk he described.

The starting point is to note that the UK’s legal position in relation to the permanence of the backstop is better than many assume. The Vienna Convention on the Law of Treaties (VCLT) provides an arguable basis on which the UK could withdraw from the backstop in certain circumstances.  There is an unresolved tension in Article 1(4) of the Protocol between the “temporary” nature of the backstop and the statement that it applies “unless and until” superseded by a subsequent agreement.  The UK and the EU have an obligation to use their “best endeavours” to conclude such an agreement.

Arguably, a right of withdrawal – in the event that the backstop ceased to be temporary – may be implied from the nature of the treaty.  In any case, unilateral withdrawal is not the only way in which a treaty may be terminated. The VCLT also guarantees the right of a party to suspend or terminate a treaty in response to a material breach of the treaty by the other party, provided that it consists in “violation of a provision essential to the accomplishment of the object or purpose of the treaty”.  There can be little doubt that the “best endeavours” obligation is essential to the accomplishment of the object and purpose of the Northern Ireland Protocol and the Withdrawal Agreement in general. EU conduct in breach of such an obligation and indefinitely prolonging the application of the Protocol could thus amount to a material breach. Faced with this situation, the UK would be entitled to invoke this breach as a ground for the suspension or termination of the Agreement and Protocol.

However, these arguments are not straightforward or clear cut. There is clearly still a significant legal risk. Nevertheless, although Parliament is not itself able to change the terms of the Agreement, or the obligations the UK would undertake by ratification, it is able to make it a condition of the Government’s freedom to ratify the Agreement that measures be taken to reinforce these arguments and so strengthen the UK’s rights of withdrawal under the VCLT.  It would be open to the Commons to approve the Agreement subject to the right of the UK to denounce the Protocol unilaterally should it turn out to be more than temporary or to suspend or terminate it for breach of the “best endeavours” obligation.  It would also be open to the House, if it were rejecting the Agreement, to make clear that it would not accept any alternative which did not protect the UK’s right to exit the backstop.

The clearest way for the Government to address Parliament’s concern would of course be by reopening with the EU the question of a unilateral right to withdraw from the backstop, and seeking an amendment of the Withdrawal Agreement to this effect. But the likelihood of that being possible is perhaps low at this late stage.

Alternatively, the Government could make a unilateral interpretative declaration to clarify and strengthen UK rights, under the VCLT, to suspend or terminate the Protocol in certain circumstances. The interpretative declaration could be that the UK will regard a breach by the EU of the “best endeavours” obligation, such that it would render the backstop more than temporary, as a material breach of the Withdrawal Agreement, and perhaps also include a statement that the UK would also regard itself as entitled to suspend or terminate the Protocol if other circumstances indicated that it could no longer be regarded as temporary.

The strength of the UK’s legal position under the VCLT depends on the centrality of the “best endeavours” obligation and on the UK making it entirely clear that it will not hesitate to suspend or terminate the treaty if faced with a breach by the EU of this obligation. Attempts by Brussels to play down this obligation may already be underway and need to be vigorously challenged if they are not to prevail.  There was a similar process in connection with the interpretation of the backstop in the December declaration. In that case London acquiesced early on in an interpretation, favoured by Brussels and Dublin, that went way beyond the ambiguous language in the declaration. It would be a serious mistake to do the same again with the ambiguity in Article 1(4) of the Protocol.