After just over a year of Brexit negotiations, the Irish border remains the biggest sticking point.

Britain cannot guarantee an open border with the Republic, as it has promised, if it insists on leaving the EU’s single market and customs union, almost all experts say. A visible border could undo years of progress toward peace, but an open border when different rules apply on either side of it is unthinkable too.

As negotiators meet in Brussels today, EU officials are adamant Theresa May’s government will have to move on Ireland if there is to be a deal that avoids Britain crashing out of the European Union in March next year.

The solution proposed by the European Commission is to keep Northern Ireland in the customs union, creating a customs border in the Irish Sea between Ulster and the rest of the U.K.

May, whose government is propped up in the U.K. parliament by the votes of 10 Northern Irish DUP MPs, has dismissed this idea as “unacceptable.”

EU officials have responded with questions that the U.K. is now working to answer.

Well then, say Brussels officials in private, the U.K. as a whole will have to stay in a customs union with the EU. To disregard Dublin's concerns about the reintroduction of a border at this stage of the talks by letting the U.K. “fudge” the issue would send an appalling message to every other small European country that when push comes to shove, Brussels does not have their back.

The Brits, led by May’s top Brexit official, Oliver Robbins, have responded with a series of micro-proposals on areas affecting the border — everything from customs, to goods, to the “single phytosanitary space” (basically, plants).

EU officials, led by Sabine Weyand, the EU’s deputy chief negotiator, have not dismissed these out of hand, according to British aides familiar with the discussions.

Instead, they have responded with questions that the U.K. is now working to answer. Robbins will travel to Brussels Monday to hold face-to-face talks with Weyand to present Britain’s response.

Much of the U.K.’s proposals build on what already exists. A “North-South ministerial council,” for instance, staffed by officials from Belfast and Dublin, is already in place to manage all-Ireland policy issues such as waterways and agriculture. A similar system may be introduced to cover areas affecting the border.

On the biggest issue of all, customs, Britain's so-called partnership proposal offers the prospect of a solution which, ironically, keeps things much as they are today.

The idea is that Britain will effectively remain in the customs union, collecting the tariffs on goods coming into the EU via Britain and paying whatever dues are owed to Brussels.

The magic comes for goods that are not destined for the EU. For these, the U.K. says it could track them and apply a different tariff — special U.K. tariffs negotiated in any free-trade deals it signs with other countries.

There are two problems: One, such a system would require the EU to trust Britain to police its customs border and pay the right dues; second, it requires a new system to monitor which goods are EU bound and which are not.

The upshot? Until this new system is ready, Britain may have to keep all its tariffs the same as the EU’s. The U.K. would legally be out of the customs union, but nothing will have changed.

Perfect, say officials. Just don’t tell the Brexiteers.

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