European Union Chief Negotiator for Brexit Michel Barnier | Thierry Charlier/AFP via Getty Images UK cannot use Northern Ireland as post-Brexit ‘test case,’ says Michel Barnier The EU’s chief Brexit negotiator says he is ‘worried’ by what he read in the UK’s proposals on Northern Ireland.

The U.K. cannot use the Northern Irish border as a “test case” for its future customs relationship with the EU, the bloc’s chief Brexit negotiator Michel Barnier said Thursday.

"What I see in the U.K.'s paper on Ireland and Northern Ireland worries me," Barnier said at a news conference, where he unveiled the EU's own position paper on Ireland-related Brexit matters. He said the British government was asking for EU law, its customs union and the rules of the single market to be suspended at the border.

"The U.K. wants to use Ireland as a kind of test case," Barnier said, adding: "This will not happen."

Barnier said the EU recognized the "unique situation and the specific circumstances of the Republic of Ireland" and that he considered it a "special responsibility" to address Ireland's concerns in his negotiations with Britain.

In a statement in response to the paper, the Irish government said: "The paper clearly reflects the continuing close engagement between Ireland and the EU Task Force ... Our priorities remain protecting the Good Friday Agreement and the peace process, including by avoiding a hard border, and maintaining the Common Travel Area."

Barnier also said that the U.K. appeared to be "backtracking" on its position on financial commitments to the EU, which it had acknowledged in July. Referring to the third round of negotiations in Brussels, in which the U.K. presented a legal analysis of the EU's position on the so-called Brexit bill, he said, "I've been very disappointed by the U.K. position as expressed last week because it appears to be backtracking."

The European Commission released position papers today on public procurement, the Northern Irish border, customs-related matters, data protection and intellectual property rights (including geographic indications).