A key criticism made by opponents of the Brexit withdrawal agreement is that the UK would be stuck indefinitely in the so-called Irish “backstop” – aimed at avoiding a hard border on the island of Ireland – with no unilateral way out.

But this assumes that the EU would want the UK to stay in the backstop indefinitely. It’s pretty clear that it would not.

In defence of her Brexit deal, Theresa May has repeatedly stressed that the arrangements for the backstop set out in a dedicated protocol on Northern Ireland would not inevitably come into force. If the agreement is approved, the arrangements would come into force at the end of the transition period if no alternative arrangements have been agreed as part of the new UK-EU relationship to be negotiated after Brexit. The transition is scheduled to end in December 2020, though could be extended once if both sides agree.

The protocol describes the purpose of the backstop provisions:

To address the unique circumstances on the island of Ireland, maintain the necessary conditions for continued north-south cooperation, avoid a hard border and protect the 1998 [Good Friday Agreement] in all its dimensions.

The backstop arrangements are therefore an agreed insurance policy, “intended to apply only temporarily”, and would only be in place “unless and until they are superseded, in whole or in part, by a subsequent agreement”. The objective “is not to establish a permanent relationship” between the EU and the UK.

No easy way out

Opponents of the backstop arrangements are justified to fear that they could remain in place for some time. There can be no guarantee that the negotiations on the future UK-EU relationship will be successfully concluded and ratified before the end of the transition. Nor can it be guaranteed that the future UK-EU relationship will remove the need for all or any of the backstop arrangements.

Read more: Can technology and 'max fac' solve the Irish border question? Expert explains

Objections to the backstop focus on three interrelated issues. First, that a decision to withdraw would have to be by mutual consent of the UK and the EU. There is currently no easy way out of the backstop.

Niall Carson/PA Wire

Second, the backstop arrangements would see the UK as a whole in a “single customs territory” with the EU, aligning its tariffs on trade with other countries with those of the EU, and obliged to “harmonise” with the EU’s common commercial policy. This would severely limit the capacity of the UK to pursue an independent trade policy.

Third, Northern Ireland would be treated differently to the rest of the UK. It would be in a closer customs arrangement with the EU and have privileged access to the single market for goods. This would require additional checks on the movement of goods from the rest of the UK to Northern Ireland, raising fears, generally overstated, for the economic and constitutional integrity of the UK.

The view from the EU

The legal advice on the withdrawal agreement provided by the attorney general, Geoffrey Cox, and published on December 5 after the government was found in contempt of parliament, maintained that the backstop’s temporary customs arrangements were “by no means a comfortable resting place in law for the EU”. Cox added: “There may be some doubt as to whether the proposed protocol is consistent with EU law.” The Northern Ireland-specific arrangements also mean that the EU would be splitting its four freedoms and creating a “dangerous precedent for other member states at risk of seeking to exit”.

Concerns about what can be established on the basis of Article 50, which governs the withdrawal process under EU law, have certainly existed in the EU. They were particularly noticeable in debates on how to interpret commitments to a backstop arrangement for Northern Ireland in the joint report of UK and EU negotiators, agreed in December 2017.

The prevailing EU view was that the backstop could only be Northern Ireland-specific. Part of the justification reflected the willingness of the EU to find “flexible and imaginative solutions” to address the unique circumstances on the island of Ireland and avoid a hard border.

However, the UK government pushed hard for a backstop that would keep the whole of the UK – rather than just Northern Ireland – in a temporary customs union with the EU. As the EU was keen to secure the conclusion of the withdrawal negotiations, a concession was made, albeit on the assumption, according to one EU source, that the arrangement would be a “baseline for the future relationship”.

Read more: 'Backstop' option for Irish border after Brexit – the difference between EU and UK proposals explained

Nothing but temporary

It follows that the EU doesn’t intend for the UK-wide customs union backstop arrangement – if it comes into force – to be anything other than temporary. It dislikes the arrangement, and the objective is to replace it with the future UK-EU relationship once that is negotiated.

It’s not an arrangement the EU originally envisaged, but one that the UK sought. It could well be that the EU might therefore be willing as a further concession to allow for the UK to withdraw from this particular aspect of the backstop arrangements unilaterally.

Yet, there is no evidence of an EU willingness to concede to opponents of the Northern Ireland-specific elements of the backstop arrangements. Here the EU has always insisted that these arrangements – including on customs – have to be part of the withdrawal agreement and will apply “unless and until” an adequate set of replacement arrangements are in place as part of the future UK-EU relationship. But this is unacceptable to many unionists, particularly in Northern Ireland, given that it would involve treating Northern Ireland differently. Other voices in Northern Ireland have far fewer reservations.

To go back on Northern Ireland-specific backstop arrangements would involve the EU prioritising the interests of a departing state over those of a member state, and publicly abandoning support for Ireland. Given the EU solidarity shown to date, this is a prospect that very few countenance.