Why is Northern Ireland/Ireland (NI/IRL) such a huge sticking point in the Brexit negotiations? It boils down to the implications of three things: leaving the Single Market, leaving the Customs Union, and upholding the 1998 Good Friday (Belfast) Agreement, writes Katy Hayward (Queen’s University Belfast).

It is worth noting that NI/IRL is a Phase 1 matter precisely because the EU is taking the UK’s intention to leave the Single Market and Customs Union seriously. There are huge ramifications of this for Northern Ireland (and as a consequence, the implementation of the 1998 Agreement). These need to be shored up and anchored at this early stage, so that they cannot be buffeted around on the as-yet uncharted seas of the future trading relationships of the UK.

So what shape could a future border take? First, the Customs Union relations to import/export of goods to/from third countries. Any border between members of the Customs Union and those outside it will require customs controls. Those controls relate to applying tariffs and quotas to goods, and ensuring that they are permitted to enter.

All goods crossing a customs border need to be declared and cleared for Exit and Entry. Electronic and pre-clearance systems can work (e.g. for Authorised Economic Operators) as means of speeding up this process, but they still entail resources, infrastructure and [the capacity for] physical inspections. In sum, a customs border is a hard border and it requires infrastructure to enforce.

For any state to say that it will not enforce a customs border – or to say that customs control is merely the choice of the other side of that border – is a derogation of basic responsibility as a trading nation. In real terms, it means exposing (and pointing to) a huge flank for criminal activity, i.e. smuggling of counterfeit or dangerous goods. That means not only a blow to the Exchequer, it is a blow to legal businesses and to communities living in the border region. This holds particular dangers in the border region of Ireland/Northern Ireland, and ones that are closely connected to the stability of the peace process. Suffice to say, a particular customs arrangements are needed here in order to avoid either a hard border or a smugglers’ paradise, with all that means for Northern Ireland.

What about the Single Market? The whole rationale for a Single Market is about creating an enormous ‘domestic’ level playing field, gaining the economic advantage of size and minimising the disadvantages of differing standards and rules within it. Any border between members of the Single Market and those outside it will thus mean friction of movement for goods, services, people and capital. By ‘friction’ I mean difficulty in crossing that border. This may come in the form of not being allowed to sell your product, work, set up a business, or reside there long term. Again, all these things have been taken for granted in Northern Ireland/Ireland.

In terms of trade within the Single Market, obstacles to the movement of goods essentially boil down to different standards. Some of these standards are harmonised across the market, others are based on mutual recognition (i.e. there can be some national differences). As the UK and EU look set to venture along on different regulatory trajectories after Brexit, the critical question is how EU member-states can be reassured that this doesn’t mean that the Irish border becomes a gaping hole in the side of the Single Market. The most comprehensive answer entails specific solution for the region (or economic zone) of Northern Ireland.

Regulatory convergence between NI and the rest of the EU would not have to mean new barriers to trade between NI and Great Britain. It is not unusual for products to meet the criteria of more than one regulatory regime; what is of critical importance is the ability to prove to traders/consumers/agencies in the receiving country that the necessary standards have been complied with. The need for mechanisms to ensure compliance, prevent divergence, and resolve disputes would have to at least be touched on at this stage in order to reassure the EU that the promise of ‘regulatory convergence’ isn’t just more ‘magical thinking’.

Finally, the 1998 Agreement isn’t about trade, but it was written with the assumption that UK and Ireland would always be partners in the EU. Aside from the complex matter of rights and equality in NI, the implementation of the Agreement after Brexit depends on the effective operation of the institutions of the Agreement and with it the continuation of cross-border cooperation (and with it the avoidance of a hard border).

To meet these, the EU needs much more than vague assurances; it needs principles (if not detailed answers) from the UK government on the following matters: How regulatory convergence with the EU will be secured, controlled and maintained in NI. And how EU rules could continue to apply in certain areas (e.g. those necessary for continued sharing of specialised health services) and how these would be protected and enforced.

The Irish government has continually said that the most simple way for this to be achieved is for the UK as a whole to stay in the Single Market and Customs Union. If the UK wishes to leave the two and if it wants to avoid a hard border, then specific arrangements need to be made for Northern Ireland. All of this centres on devolved competence to Northern Ireland, securing the institutions of the Agreement, strengthening the capacity of Northern Ireland sea/air entry ports for customs checks, and allowing the jurisdiction, say, of the EFTA court. No such arrangements would have any effect at all on the ‘constitutional integrity’ of the United Kingdom.

Without any specific arrangement for Northern Ireland as it leaves the EU, talk about ‘avoiding a hard border’ and ‘upholding the Belfast Agreement’ is either empty rhetoric or dangerous delusion.

This post represents the views of the author and not those of the Brexit blog, nor the LSE.

Dr Katy Hayward is Reader in Sociology & Senior Research Fellow, Senator George J. Mitchell Institute for Global Peace, Security and Justice at Queen’s University Belfast.