Chief EU negotiator for Brexit Michel Barnier | Francois Walschaerts/AFP via Getty Images Michel Barnier pours cold water on UK Brexit backstop plan Under the UK proposal, Britain would remain within a partial customs union with the EU for a limited period.

There was a theory in London that Michel Barnier might cut the U.K. some slack on its latest Brexit proposal. The EU Brexit negotiator just shot that idea down.

The theory went that Theresa May would get credit in Brussels for having pushed back against Brexiteers in her Cabinet — including a threatened resignation by Brexit Secretary David Davis on Thursday — to deliver a proposal to Barnier that could at least get a hearing.

He didn’t reject it out of hand. But the best he could muster was at least the Brits had delivered something on paper. “It’s good to see the U.K. engaging with us by proposing text,” he said.

The U.K.’s proposal for a "temporary backstop" solution to Ireland “doesn’t correspond” to the EU’s wishes, Barnier said on Friday, adding that May had agreed on the need for it, and “there is no way we will go backwards.” Barnier said he would discuss the plan with Davis on Monday morning when the two meet for talks in Brussels.

His remarks, at a press conference in Brussels, are the first substantial reaction to the U.K.’s alternative backstop proposal to avoid a hard border in Northern Ireland if negotiators fail to reach agreement.

Barnier raised a catalogue of objections to the British proposal, questioning whether the U.K.’s idea to avoid a hard border in Northern Ireland would work because it is time limited — a key stipulation from Davis.

“The U.K. calls this arrangement temporary,” said Barnier. “How does that fit with the need to secure the absence of a hard border in all circumstances?”

“Backstop means backstop,” he repeated three times during his remarks.

Switching into English to deliver his verdict on the paper, the EU negotiator said even the U.K. government recognizes that the proposal cannot qualify as a “backstop” because the issue of full regulatory alignment is not addressed.

“I repeat that we need regulatory alignment to avoid a hard border,” he said.

And he questioned whether it is feasible for the U.K. to continue to benefit from EU trade agreements. “Does that mean that we will have to reopen, renegotiate or even re-ratify our existing agreements?” he asked.

He also said that it is hard to see how a customs arrangement could be extended to the entire United Kingdom. “Our backstop cannot be extended to the whole U.K. Why? Because it has been designed for the specific situation of Northern Ireland,” he said, adding that what is “feasible” for the relatively small territory of Northern Ireland is not necessarily feasible for all of the U.K.

Under the U.K.’s backstop proposal, Britain would remain in a partial customs union with the EU beyond the end of the agreed transition period in December 2020. It would continue to apply the EU’s external tariff regime but not be bound by the bloc’s Common Commercial Policy, meaning it could in theory implement its own trade deals.

The document contains what is essentially a sunset clause, but it is framed more as an aspiration than a legal cutoff date. “The U.K. expects the future arrangement to be in place by the end of December 2021 at the latest. There are a range of options for how a time limit could be delivered,” it reads.

In remarks that were apparently aimed at his opposite number, the chief negotiator rejected the idea that the EU could be blamed for the outcome of Brexit.

In a speech on security on Wednesday, Davis said: “It’s sometimes said that the limits of our cooperation have been set by the United Kingdom … I don’t agree. The European Union does have choices.”

Without mentioning the U.K. negotiator by name, Barnier said, “Some in the U.K. seek to make us responsible for the consequences of that decision,” he said. “We won’t let ourselves be intimidated. I won’t let myself by intimidated by this form of blame game.”

The U.K has asked to leave the EU but it is now seeking a status quo, “a form of continuity that is rather paradoxical,” Barnier said. Though progress has been made on several separation issues, Barnier said there is a “lot of work” left on several issues including data protection and the need to protect data “that have already been exchanged,” as well as the protection of geographical indications — a form of brand protection on products such as Champagne — for which “we still have not obtained any British position.”

Barnier was asked to comment on leaked comments from U.K. Foreign Secretary Boris Johnson, who reportedly told a private dinner of Conservative supporters earlier this week that predicted an imminent “meltdown” in relationships with Brussels.

Barnier didn’t take the bait. “I always listen to him carefully. Listening to him is always stimulating,” he said.

Responding to Barnier’s remarks, a U.K. government spokesperson said: “The prime minster has been clear that we will never accept a customs border between Northern Ireland and the rest of the United Kingdom. We are also committed to maintaining the integrity of our own internal market. That position will not change. The Commission’s proposals did not achieve this, which is why we have put forward our own backstop solutions for customs.”