The EU, and above all its member state Ireland, insist that no hard border can be created with Northern Ireland, which is part of the U.K., once Britain leaves in March. That means no border posts or customs checks after Brexit to protect economic links and the hard-won peace on the island of Ireland.
Prime Minister Theresa May's proposal would align British trade rules with those of the EU until a permanent deal is worked out, and her government has said that it expects such an agreement to be in place by the end of Dec. 2021 at the latest.
"I think it raises more questions than it provides answers," Michel Barnier told reporters, recalling that a Brexit withdrawal agreement must be sealed by October to leave time for parliaments to ratify it before the March 29 deadline.
"We are today at a time of decisions and choices. Time is running out," Barnier said. "We must conclude this agreement in autumn, in a few months." Should Britain's proposal be unworkable, EU nations insist that a "backstop" remain in place to keep Northern Ireland within Europe's customs arrangements. Barnier said he and his team are still studying Britain's offer, but that London appears to want to keep the whole of the U.K. in parts of the customs union.
"Our backstop cannot be extended to the whole U.K.," Barnier said. He said it is designed uniquely for Northern Ireland In a statement in London, the British government 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."
It said that "the Commission's proposals did not achieve this, which is why we have put forward our own backstop solutions for customs," and that Barnier himself has acknowledged that discussions will continue on the British proposal.
Barnier's remarks in Brussels, following a new round of Brexit talks, come as tensions mount within the British government over how best to handle its departure, the first time an EU member state has ever left the world's biggest trading bloc.
In a recording obtained by BuzzFeed news, Foreign Secretary Boris Johnson was quoted as telling Conservative party donors that May's government is ready to start playing hardball with the EU, just three weeks before Brexit is discussed among European leaders.
"I think Theresa is going to go into a phase where we are much more combative with Brussels," Johnson said. "You've got to face the fact there may now be a meltdown. OK? I don't want anybody to panic during the meltdown. No panic. ... It's going to be all right in the end."
Asked for his reaction, Barnier said that he wonders if Britain "sometimes feels a certain nostalgia about leaving the European Union because it seems to want to remain inside practically everywhere without ever respecting the regulatory framework."
He said the EU has drawn up its negotiating stance by taking careful account of Britain's demands. "We respect Britain's red lines. I would like the British government to respect its own red lines as well," Barnier said.
Barnier said that while some progress has been made, several issues remain to be resolved before the 28-29 June EU summit.
Kirka reported from London.