To avoid a hard Border on the island of Ireland after Brexit you need to find a way to avoid two separate but connected sets of checks. Customs checks ensure the correct duties and tax are paid and goods shipments are controlled and monitored. Other checks are needed on product regulations and safety, particularly on animal health and food. At borders across the world, these separate checks normally take place as part of one process.

The plan being put forward by Boris Johnson and now published proposes to split this problem in two. It would require a customs border between Northern Ireland and the Republic and a regulatory border in the Irish Sea between the North and Britain. Apart from the obvious issue – the need for Irish border customs checks – it is messy, looks to have serious practical problems and is unlikely to find favour in Brussels.

The first key issue to watch is whether the EU side decides whether this is the basis for formal negotiations in the run up to the EU Summit in mid-October.

Johnson makes clear that the UK sees this plan as more than a backstop. It sees it as the way things will operate after the end of the transition period in 2021. For Ireland, this would mean signing up to the certainty of the North moving into a different customs regime and the need for checks and controls – not just the possibility that they might happen if future talks don’t work out. And there would also be the possibility that regulatory rules might, in time, diverge too.

The EU’s original plan for the backstop – the guarantee that there will not be a hard border – was that the North would effectively remain part of the EU’s trading bloc. The North would be in the EU customs union and aligned with whatever single market rules were necessary to avoid a hard Irish border. All checks would then take place in the Irish Sea, as goods entered the North from the UK. In a later iteration all of the UK would have stayed aligned to the customs union.

DUP objections and a determination that the UK leave the EU trading bloc behind led to the “ditch the backstop” rhetoric and the latest plan. Under the Johnson proposal, Ireland would be one zone for animal and food health and safety and for regulations covering manufactured goods, avoiding the need for regulatory checks on the Irish Border on cattle, milk, industrial products and so on. This would require stepped up checks on animals, food and other goods crossing the Irish Sea to the North.

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However Johnson is insistent that the UK, including the North, remains in one customs union and that this is separate from the EU. This is to allow the UK to do its own trade deals with other countries. This means customs checks and controls would be essential on goods entering the Republic from the North, to ensure duties are paid, to avoid smuggling and to ensure the contents and movement of trucks are monitored..

Technology

The UK says the use of technology and advanced processes – and some exemptions for SMEs – mean no actual physical infrastructure would be needed at or near the Border. The EU will not sign up to this, nor to the suggestion that how it would work can somehow be worked out during the transition period. Protecting the single market is a vital goal.

Customs checks almost certainly would require a physical location to check goods entering the Republic and some advanced processes and infrastructure – such as cameras – to monitor movements. This does not happen anywhere in the world without some infrastructure.

Nor is this trivial. Minister for Finance Paschal Donohoe has pointed out that a key issue for the Republic is to ensure that Irish goods can continue to be accepted as “Irish” in EU markets – in other words that goods from the UK or beyond are not entering the single market through some kind of back door. This is central to Ireland’s entire economic strategy and is why the Government accepts that checks would be needed in the event of a no-deal.

In December 2017, as part of the Brexit talks, the UK committed to avoiding infrastructure at or near the Border and to protect the all-island economy and the Belfast Agreement. While there is scope for argument over exactly what these words mean – what is “at or near the border”, for example – it is clear that this plan ditches these commitments.

There are other reasons this will cause problems in Dublin and Brussels too. By giving the Stormont Assembly, now defunct, a role in deciding after four years – in 2025 – whether to remain aligned to single market rules, or align with UK rules, it appears that the DUP would thus have an effective veto. This could then trigger the need for stepped-up checks at the Irish border, if Stormont voted to return to the UK regulatory regime.

“Two borders for four years” is the catchphrase. So this is a time-limited commitment to regulatory alignment on the island of Ireland, rather than an enduring one. And it is a clear statement that the North will leave the EU customs union.

For the DUP, it may look like a defendable compromise. But for businesses in the North it would involve border checks in both directions, with one business group, Manufacturing NI, tweeting last night that “we’re thrown under the bus” and the initial reaction of the North’s businesses is very negative.

Johnson now says that if the EU does not negotiate on the basis of this “final offer”, the UK will push ahead and leave under a no-deal on October 31st. We wait to see now if this latest plan leads to negotiations. If not, whether he can achieve the October 31st exit , given the legislation passed by the Commons legally ruling this out, now looks like the vital question.