Henry Newman is Director of Open Europe.

Last week, I set out how the Prime Minister should seek improvements to the Brexit deal before Sunday’s Brexit summit. She got halfway there. On the Political Declaration, she succeeded in substantially improving the document – achieving a clear choice between a Canada plus arrangement, and a closer Chequers minus plan, with Canada plus as the default. However, she did not secure changes to the Withdrawal Agreement. The ineluctable problem she now faces is that when Parliament rejects her deal on the 11th December she will have a tough choice: seek further changes in Brussels or prepare for No Deal.

Both the UK and EU will be extremely reluctant to change agreed texts, but they may be left with little alternative if Parliament says no. We have been here before – David Cameron’s deal worked in the theory of Brussels, but fell apart on contact with Westminster politics. Theresa May’s deal is actually better than I had expected in various ways. Yet even in areas where she has secured victories, Downing Street is failing to cut through noisy cries of betrayal. And because MPs have begun to doubt her motives, the Prime Minister faces an uphill battle to explain how the deal would work.

The most egregious part of the deal remains the Northern Ireland backstop. Yet the only path to a Brexit which certainly avoids a backstop is not Norway plus or Super Canada but No Deal. Those demanding that the Prime Minister simply insist that she won’t accept a backstop haven’t paid enough attention to Brussels. And it’s far from clear that changing Prime Minister would make anything easier. It would probably further radicalise the Commission against softening its position.

But without changes the deal seems certain to fail in the Commons. Since the Cabinet meeting which first approved this divorce deal on the 14th November, there has been disagreement amongst May’s inner circle as to whether to seek further changes. Her senior team tell me that the EU is not going to start the negotiations all over again. Yes. But that’s not quite the same as saying that, in extremis, modest but material changes are off the table. European diplomats have no real plan B, but then neither does the Government – other than No Deal.

One of the changes I’ve proposed to the backstop is a Stormont “lock” – a mechanism for consulting the Northern Ireland Assembly and Executive, the institutions of the 1998 Belfast (or Good Friday) Agreement, about new regulatory barriers within the UK. Back in December both the UK and EU agreed a Joint Report, paragraph 50 of which noted that in the backstop “the United Kingdom will ensure that no new regulatory barriers develop between Northern Ireland and the rest of the United Kingdom, unless, consistent with the 1998 Agreement, the Northern Ireland Executive and Assembly agree that distinct arrangements are appropriate for Northern Ireland”. For some reason, this dropped out of the final text. It should be re-introduced.

How would a Stormont lock work? The purpose would be to create a mechanism to question new EU acts – it would specifically address the flow of new rules, not the stock. It would only apply if the UK was in the backstop, and if the Assembly was restored. It could be designed so it gave an option to vote against a new rule, rather than requiring affirmative votes on every new rule.  You could require a strong majority vote to trigger the lock (although that could entail reforms to the petition of concern process).

There are already areas where there are different rules in Northern Ireland compared to the rest of the United Kingdom – for example on same-sex marriage and abortion (although Northern Ireland could choose to align with Great Britain in those areas). In future, if the backstop was in place, there might be areas where it made sense for Northern Ireland to choose to diverge from Great Britain, and instead align with EU rules covering the rest of the island of Ireland. This would likely be the case, for example, on rules affecting the single energy market or agricultural standards.

What is not acceptable is for new rules and regulations to be imposed over the heads of Northern Ireland’s elected representatives without an ability to say no. That’s not devolution, and it’s not democratic. And it’s not clear how imposing rules on Northern Ireland would be compatible with the European Convention of Human Rights. The landmark Matthews v United Kingdom (1999) case found that people have to have representation in a legislature enacting laws. Karen Bradley, the Secretary of State for Northern Ireland, recognises concerns about the backstop, saying “rules in Northern Ireland cannot change without rules changing either here in Westminster or Stormont. They cannot be automatically changed by another third party” [i.e. Brussels].

So what would happen if Stormont voted against a new EU rule? The issue would be referred to the Joint Committee comprised of UK and EU representatives. Under the existing terms of the Withdrawal Agreement, the Joint Committee already has to agree every new EU ‘act’ which would apply to Northern Ireland. So under Theresa May’s deal the UK can already resist new regulations, directives and decisions from the EU which would have to be applied in Northern Ireland. But an explicit role for Stormont should be added.

If the Stormont lock was engaged the Joint Committee could take several possible steps. One would be just to not apply the new act in Northern Ireland (nor, of course, in the rest of the United Kingdom) while working to resolve any issues this created. Another option would be, with the consent of the UK Parliament, to apply the act across the whole UK (meaning Westminster voting to keep the UK in step with the EU). A third option could be for the the Irish Republic to decide to seek a derogation from the EU for that new act. There are already existing EU precedents for this – for example, Malta has provisions limiting the purchase of second homes.

We are now in the unhappy position where the current deal has satiated the concerns of the nationalist community and the Irish Republic (who nonetheless remain opposed to Brexit), but has left Unionists (the DUP, the UUP, and others) unhappy. This is highly problematic because the deal could put at risk the principle of consent which was at the heart of the Belfast Agreement – precisely the agreement that the EU was claiming to be so concerned to protect by creating the backstop in the first place. A Stormont lock would go some way to addressing these concerns.