EU officials working on one of the thorniest of Brexit conundrums — how to create a "seamless border" in Ireland — are exploring how regular cross-border traders could be pre-vetted to reduce bureaucracy while allowing some random customs checks away from the frontier itself.

The highest ranking officials on each side — Oliver Robbins for the U.K. and Sabine Weyand for the EU — are personally overseeing negotiations about the border between Northern Ireland and the Republic of Ireland to the south, so important is agreement on this question to the overall success of the talks, which began last week.

Both sides recognize the sensitivity of the Irish border and do not want to create a hard frontier with border posts that could become targets for dissident Republican groups.

The economic stakes are also high because trade across the border is worth £43 billion and more than a third of Northern Irish exports go via land to the south. The U.K. says it wants to withdraw from the EU customs union which, unless the two sides agree special arrangements, would insert a barrier to the current frictionless trade between the two countries.

POLITICO has spoken to four officials involved in technical preparations who said that concrete solutions are being worked up that can be fed into the talks.

"We're trying to protect the single market and [prevent the Irish border becoming] a back door to import and export goods from third countries without any checks," one of the officials said. "At the same time [we want to avoid] any disruption of all economic operations between the two parts of the island."

One option is for companies in Northern Ireland to become what is known as an "authorized economic operator" after Brexit, according to a senior Commission official aware of the technical discussions.

Achieving this status allows businesses operating beyond the EU's borders to enjoy trade benefits as long as they can meet a wide range of criteria based on international standards surrounding health and safety. Any customs duties are paid quarterly, which allows for priority treatment during the customs clearance stage — and crucially no need for checks at the frontier itself.

Regulating goods and vehicles belonging to businesses that are not authorized operators and those carrying goods from countries outside of Europe across the Irish border poses a trickier problem however. For those goods, the EU could use a "risk-assessment approach," the Commission official said. That would entail random checks on vehicles crossing the border in order to clamp down on goods that do not comply with EU health and safety regulations from entering the zone through the back door. Such vehicle stops and checks could crucially occur a significant distance from the physical border itself though.

Arrangements like this have precedents on the fringes of the EU. There is no hard border between Germany and Switzerland for example but officials carry out random spot checks on freight. Similarly, Norway and Sweden have close cross-border arrangements to avoid unnecessary bureaucracy.

Another official said brainstorming has been underway in Dublin on the possibility of conducting on-site veterinary controls of cattle and sheep going for slaughter to avoid needing paperwork checks at the border. Such processes could be rolled out with relative ease as vets are already a part of local communities in Ireland, the official said. Applying this approach to goods such as raw milk will be harder though because of the lack of inspectors in remote areas.

Though the ideas have yet to be formalized or made it into any official EU position paper, officials said there is widespread accord among the EU27 that Ireland can be treated as a special case in the Brexit talks — a position that was affirmed in the negotiating directives published by the EU. These state "the unique circumstances and challenges on the island of Ireland will require flexible and imaginative solutions." Prime Minister Theresa May has also said that Britain wants "to avoid a return to a hard border." The Democratic Unionist Party, which reached an agreement Monday to prop up the Conservative government in Westminster, are also against the return of a hard border.

Last week, Ireland’s new Prime Minister Leo Varadkar said that Brexit talks should refrain from changing the status quo on the Irish border. “Our objective is a very clear one, and it’s a very simple one: that there should not be an economic border between Northern Ireland and the Republic of Ireland,” he said arriving in Brussels for an EU leaders' summit.

Asked about the ideas formulating in Brussels, a spokesperson for the U.K.'s Department for Exiting the European Union said: "We welcome the European Council and Commission's commitment to work on flexible and imaginative solutions to avoiding a hard border."

"We are determined to protect the everyday movement of goods across the border, and we absolutely recognize the importance of this to the economy in Northern Ireland," the spokesperson said.