Tusk will join German Chancellor Angela Merkel, Irish Prime Minister Enda Kenny and other members of the conservative European People's Party group at a long-planned meeting in Malta on Thursday that now takes place against the backdrop of Brexit.

“This is Day1 of a very long and difficult road,” EU negotiator Michel Barnier tweeted.

Nine months since Britons voted to terminate their 44-year run in the EU, May initially struck a conciliatory tone in a letter to Tusk that invoked Article 50 of the Lisbon Treaty. She cast the breakup as a chance to forge a new “deep and special partnership” and acknowledged she cannot cherry-pick the best bits of EU membership.

But it soon became apparent the two sides were as far apart as ever. The niceties were followed by a bid for a “bold and ambitious” duty-free trade pact, which for the first time May suggested should encompass finance, a key plank of the U.K. economy that she argued is critical for the EU too.

Keen to safeguard tens of thousands of banking jobs and the City of London's status as a global financial hub, the premier also echoed industry requests for an early commitment to a transition to smooth the break and avoid a “cliff edge” of uncertainty.

That's also a sign she realizes the deal she wants cannot be sealed within the time frame she still maintains is possible. It took the EU more than seven years to secure an accord with Canada and it included only partial access for the finance sector.

A First

“If the U.K. succeeds in agreeing the sort of trade agreement with the EU that the PM wants, it will be a first in global trade,” said Phillip Souta, head of policy at law firm Clifford Chance.

The European Parliament may also prove an obstacle. It said any transition conversation should await “substantial progress” on an exit agreement and then the stopgap shouldn't last longer than three years.

But May's lauding of the mutual advantages of free trade came with a hint of menace. She cited “security” 11 times in a letter written a week after London's worst terror attack in more than a decade reminded European nations of their shared vulnerability.

If “we leave the European Union without an agreement the default position is that we would have to trade on World Trade Organisation terms,” she wrote. “In security terms a failure to reach agreement would mean our cooperation in the fight against crime and terrorism would be weakened.”

May's office insisted that the U.K.'s support for NATO's operations bolstering European defense was not in doubt. The new security deal the premier wants would cover only specific EU programs such as the U.K.'s membership of the European Arrest Warrant and Europol, an information-sharing network, said James Slack, May's spokesman.

Home Secretary Amber Rudd nevertheless underlined the point that Britain views security as very much in play.

“We are the largest contributor to Europol, so if we left Europol, then we would take our information — this is in the legislation — with us,” she told Sky News. “The fact is, the European partners want us to keep our information in there because we keep other European countries safe as well.”

Nick Macpherson, the U.K. Treasury's former top civil servant, tweeted that “crime and terrorism don't respect borders. It is not a credible threat to link cooperation to a deal.” Rupert Harrison, a former government adviser now at BlackRock, called the juxtaposition “punchy.”

However, the German chancellor and others weighed in forcefully to remind the U.K. that the early part of negotiations has to be about the talks themselves. Tusk insisted the first phase must focus on “key arrangements for an orderly withdrawal.”

Merkel promptly backed him. “In the talks, we first have to figure out how to disentangle” the bonds, she said in a speech in Berlin. “Only when those questions have been dealt with, hopefully soon, can we talk about how to craft our future relationship.”

Tusk's job for the next 48 hours is to flesh out the EU's strategy by drafting guidelines for Barnier to be pored over by EU leaders on April 29.

Differences over money also lingered. With the U.K. dismissive of the suggestion that it must pay a bill of around 60 billion euros ($65 billion), the European Parliament said in a draft resolution that the U.K. must “honor all its legal, financial and budgetary obligations.”

May indicated two can play the money game as she said Britain has rights as well as obligations and that a “fair settlement” was merited.

“There's certainly going to be a dogged fight about that,” Austrian Chancellor Christian Kern said.

European Commission President Jean-Claude Juncker made his own dark prediction. The Britons, he said, made “a choice they will regret one day.”

Bloomberg News

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