LONDON — Less than a week after the U.K. left the European Union late Friday night, the mood has already soured — with British and EU officials trading cross-Channel barbs over a possible trade deal and the future of the U.K.

Brexit night on Friday, January 31, marked the end of a remorseful but relatively friendly period of farewell and triggered a new, much more belligerent tone from both London and Brussels.

Before the weekend was out, U.K. Foreign Secretary Dominic Raab accused the EU of “trying to shift the goalposts” ahead of trade talks and Irish Prime Minister Leo Varadkar called U.K. plans for its diplomats to sit apart from EU counterparts in international forums “a little bit petty.”

If that wasn’t enough, recently departed European Council President Donald Tusk told a television interviewer that Brussels would be “enthusiastic” about an independent Scotland one day joining the EU. Never mind that this would mean the dismemberment of the U.K. It prompted Raab (again) to accuse Tusk of being “irresponsible.”

To some extent a change of tone was inevitable. Since the Brexit deal was struck in October, London and Brussels have had a common goal: ratifying the deal and guaranteeing the U.K.’s orderly departure.

The current tit-for-tat is really a battle to set the parameters of the trade talks to come.

On February 1, that shared endeavor ceded into the past, to be replaced by a new dynamic. The U.K. is now a third country, on the opposite side of a negotiating table where it and the EU will both ruthlessly pursue their own self-interest.

The current tit-for-tat is really a battle to set the parameters of the trade talks to come. The EU’s chief negotiator, Michel Barnier, has said that the U.K. aligning with EU regulations — the so-called level playing field provisions that would prevent it undercutting the EU on environmental, workers’ rights and other standards — is a condition for achieving an “ambitious” trade agreement covering goods and services.

Boris Johnson, in a speech on Monday, chimed with Raab; the Canada-style free trade agreement they seek does not require full alignment with EU rules, he insisted, and questioned why, if it did, the U.K. should not demand the same of the EU. “I hope our friends will understand that what is sauce for the goose is sauce for the gander,” he said.

The prospect of the two sides failing to find common ground has prompted London to come up with a new euphemism: If they don’t get Canada, they’d be happy with an “Australia-style” Brexit. Cue more diplomatic barbs from EU trade chief Phil Hogan, who pointed out the obvious: “We do not have an agreement with Australia,” he said. “I think that’s code for no deal.”

In truth, it was to be expected that both sides would start negotiations with a relatively hard line. But time is very short if a trade deal is to be in place in time for Johnson’s self-imposed end-of-year deadline. There is little time to waste on saber-rattling, said former European Commissioner for Trade Peter Mandelson, who advised Johnson on BBC Radio 4, “Be calm, it’s a long journey, take it step by step, sector by sector and dial down the rhetoric, the megaphone diplomacy.”

In the yah-boo world of Brexit, that’s a plea that may fall on deaf ears.

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