Brussels is used to training its fire on unwanted Brexit proposals from London — but diplomats had to scramble Monday to deal with a curveball from within their own ranks.

Polish Foreign Minister Jacek Czaputowicz told the Rzeczpospolita newspaper that "courageous actions" are now needed to find an agreement to avoid a no-deal Brexit. And he added: "If Ireland turned to the EU about changing the agreement with Britain with regard to the provisions on the backstop so that it would only apply temporarily — let’s say five years — the matter would be resolved."

The idea that the Northern Ireland backstop — which is designed as a fail-safe mechanism to avoid the need for a hard border in all circumstances — could have a time limit would mean that Dublin and Brussels abandon the reddest of their Brexit red lines. It was an incendiary suggestion that, just hours later, prompted questions in the House of Commons from Brexiteer MPs to Theresa May, following her announcement of the government's Plan B.

The prime minister said she looked forward to "exploring" the proposal "in more detail."

Brexiteers have been saying for months that if the U.K. waited long enough, the EU27's impressive (and to some unexpected) unity would begin to crack. Czaputowicz's suggestion, they hope, is the first indication that Brussels will eventually throw Ireland under the bus when a no-deal Brexit begins to look like a serious possibility.

"By now we are quite used to this minister's comments. It is not the first time he breaks rank" — EU diplomat

Not so fast.

At best, the reaction from EU ministers and diplomats ranged from a shrug to weary consternation that one of the EU's regular contrarians has chosen such a crucial juncture to throw a spanner in the works.

"By now we are quite used to this minister's comments," said one EU diplomat. "It is not the first time he breaks rank. It's surprising how Poland relies on the solidarity of others but never shows it when other member states need it."

"What they fail to see is that there will be no solution for the Polish citizens in the U.K. without a sustainable, acceptable solution for the Irish border," the diplomat added.

Other officials appeared displeased that the Polish minister offered his opinion at all. "For the EU on Brexit, the ones entitled to talk are [Commission President Jean-Claude] Juncker, [Council President Donald] Tusk and [EU negotiator Michel] Barnier. Not single member state's ministers," said a second EU diplomat.

"I think it is dangerous," said a senior official from an EU27 country. "We stand behind Ireland and it is up to them only to accept any change in the backstop."

In London, May presented her Plan B to MPs following the crushing defeat of her Brexit deal last week. Rather than pursue a softer Brexit position to entice opposition MPs to back her, she instead doubled down on her existing strategy.

She said there are two "core concerns" with the backstop: "The fear that we could be trapped in it permanently; and concerns over its potential impact on our union if Northern Ireland is treated differently from the rest of the U.K."

“So I will be talking further this week to colleagues — including in the DUP [Democratic Unionist Party] — to consider how we might meet our obligations to the people of Northern Ireland and Ireland in a way that can command the greatest possible support in the House," she said. “I will then take the conclusions of those discussions back to the EU.”

With May seeking, yet again, to find movement in Brussels on the backstop, Czaputowicz's intervention might look like a timely olive branch.

The DUP's Westminster leader, Nigel Dodds, called it a "constructive attempt to re-energize talks in good faith."

"Poland is facing up to reality and being pragmatic," he said.

But even No. 10 Downing Street appears skeptical that the Polish intervention is a sign the EU is ready to negotiate.

When asked whether the comments are an opening for talks, a Downing Street spokesman responded less than enthusiastically: “We want to see a resolution to this … the conversations the prime minister has been having with European counterparts indicate a shared desire that when we leave the EU we do so with a deal.”

In public, EU ministers insist that no one minister can change the EU's negotiating position.

"For us, the Commission negotiates, and it will stay this way," German Foreign Minister Heiko Maas said after a meeting of EU ministers in Brussels. "It is important that the EU stays united in this. So we should not press forward with individual proposals," he said, noting that "we will wait [and see] what will happen in London and then surely talk to our colleagues in the U.K."

Ministers emphasized that the bloc remains united in its formal stance. The EU27's cohesion is "not yet" eroding, Austrian Foreign Minister Karin Kneissl told reporters.

"Until now, for the past two years, we've had this very high degree of cohesion among the 27, and I deem it's more than useful to keep that cohesion and not to start making bilateral announcements," she said, adding that the Withdrawal Agreement "is still the document which is our basis for any other discussion."

"I don't think that reflects EU thinking in relation to the Withdrawal Agreement" — Simon Coveney, Irish foreign minister

Asked about the Polish minister's comments, Irish Foreign Minister Simon Coveney said that Czaputowicz had raised the proposal in Dublin in December.

"I don't think that reflects EU thinking in relation to the Withdrawal Agreement," Coveney said, adding that he understands the Polish foreign minister's concerns over the potential damage of no deal.

Some diplomats noted that the Poles have long been the weakest link in EU unity, in part because just under a million Polish nationals live in the U.K.

“Objectively, the Poles are the most nervous on the issue of Brexit, so they are the most flexible partners for the U.K.,” said a third EU diplomat. “They are very nervous when it comes to preserving the rights of their citizens in the U.K.”

But other senior Polish officials appeared to play down the remarks, insisting that Warsaw is committed to EU27 cohesion.

"We have to do our best to avoid no-deal Brexit," Polish European Affairs Minister Konrad Szymański told POLITICO. "But it can be resolved only by all 27 member states together. Poland, like many other countries, is looking for solutions. But there is no danger for EU unity in Brexit talks."

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