The writer, a lawyer and commentator, is an FT contributing editor

The legal and political framework for the Northern Ireland trade deal announced in Windsor by the UK and EU on Monday does not replace a blank slate. Instead, it fits into and recasts the Good Friday Agreement of 1998 and the Northern Ireland protocol of the 2020 Brexit withdrawal agreement.

Indeed, the two sides have expressly agreed to formally refer to the amended protocol as the Windsor framework. This will not just be a snappy nickname but a defined term.

One key legal change proposed is the “Stormont brake” for dealing with disputes. The existing protocol does contain the Article 16 provision that allows either side to take unilateral “safeguarding” measures in the event of serious difficulties with the implementation of the protocol or when trade is diverted. But this has never been fully used and the UK chose not to invoke it, instead seeking to introduce domestic legislation that would enable it to break the terms of the agreement.

A dispute resolution procedure that is not deployed when there is a dispute is not much use, and it was plain that a new system was required. This is what the Windsor framework will provide in general, and what the Stormont brake will give comfort on in particular.

The brake only applies to proposed new EU legislation — it does not affect that already effective in Northern Ireland. And nothing in it removes the jurisdiction of the European Court of Justice as the final arbiter of EU law in the province.

If the UK is concerned about new EU legislation that affects Northern Ireland, then it can notify the EU. It will have to explain why it considers the legislation different from what went before and also how it “would have a significant impact specific to everyday life of communities in Northern Ireland in a way that is liable to persist”.

This latter requirement is a high threshold — in the legal document it is referred to as an “emergency brake mechanism”. The UK will have to show not only a significant impact but also the breadth of this impact and its duration.

This is not merely a redressed Article 16 threshold; the intended legal effect appears to be different. Under the current protocol, any safeguarding measure can only be adopted when strictly necessary to remedy a situation and is subject to constant review and structured negotiations. Under this proposal, any new EU legislation that is complained of must be challenged within two weeks of the notification. And while Article 16 provides a regime for temporary remedies, the Stormont brake is, in effect, a veto on legislation altogether.

Before operating the emergency brake, however, the UK must follow a specified procedure. And for this to happen, the Northern Ireland executive will first need to be restored and operational. Then 30 members from at least two parties of the 90-strong Northern Ireland legislative assembly (MLAs) must notify the UK government that they wish the brake to be applied.

This can only be done in the “most exceptional circumstances and as a last resort, having used every other available mechanism”. And, as well as showing that the impact requirements are fulfilled, the MLAs must show that they have consulted businesses and civic society, and participated in any prior consultation exercises carried out by the EU.

All this means it will be difficult for the Stormont brake ever to be applied. Perhaps the provision is intended as a reassuring ornament rather than a practical instrument. But that was also once said about Article 50 of the Treaty on European Union, which the UK invoked to leave the EU.

It is important therefore that the mechanism is capable — and is seen as being capable — of actually being used. The safeguards provision in the existing protocol is so hedged with qualifications that it has not been. The concern has to be that the proposed brake will also end up as a similarly academic solution. If it is — or is seen as — impossible to apply, then the proposal solves nothing. The new mechanism must be an instrument, not an ornament.

The EU will be reluctant to lower the thresholds or to make the conditions for the brake less onerous. But it may have to move on this, unless the unionist community in Northern Ireland can be convinced this new mechanism will make a real difference.