Chancellor Angela Merkel

Britain remains a key ally even though it is leaving the EU, the German government said Wednesday, while warning of tough negotiations ahead.

Calling for swift clarity as British Prime Minister Theresa May triggered the exit process, Berlin also cautioned that uncertainty unleashed by the talks could be “poison” to both citizens and commerce.

“We must not forget that the UK is still a partner, in NATO and in Europe,” Chancellor Angela Merkel’s spokeswoman Ulrike Demmer told journalists, adding that London’s Brexit notification would offer clues on how Britain planned to handle the divorce process.

“On this basis, the 27 member states and EU institutions will define their interests and aims,” Demmer said, adding that Berlin was “well prepared” for the coming negotiations.

Foreign Minister Sigmar Gabriel acknowledged that the talks would “certainly not be easy for both sides.” Although the split may generate “bad feelings,” he said that should not form the basis of Britain’s future relationship with the EU’s remaining 27 members.

“The sentence often used in private divorces, ‘let’s stay friends,’ rings true in this case,” said Gabriel.

“Britain remains our neighbor, like the European Union is for Britain. We need each other. We should do everything to maintain a good and friendly relationship in the future,” he added. At the same time, a Foreign Ministry source also pointed out that “a close friend is still somewhat different from remaining part of the family of 27.”

“That is hopefully also clear to the Britons,” said the source, adding that both sides are aware that “Britain’s decision to separate from the EU at a time when the old order seems to be breaking apart … is reckless.”

Underlining what is at stake, Foreign Ministry spokesman Martin Schaefer emphasized that “uncertainty is poison for the people — the EU citizens, Germans who live in Britain and what their future status would be, likewise for British citizens living in the European Union.”

“Perhaps it’s even more poisonous for economic trade and investment relations,” he added, questioning if London “really understood what kind of impact there could be for the British economy when all these questions have to be addressed,” and noting the “damn tight” two-year negotiation period.

“We are proud of the clear, unanimous stance of the EU 27, that they stood their ground that there would be no pre-negotiations,” he added.

“They begin now.

Next steps

Here are the key steps ahead:

• European Council President Donald Tusk will issue draft “negotiating guidelines” on Friday. He is due to give a press conference with Maltese Prime Minister Joseph Muscat on Friday in Valletta. These are overall political red lines for the next two years and will be circulated to the capitals of the 27 remaining EU countries. Diplomats known as sherpas make further preparations and then ministers will finalize the guidelines in late April.

• Even if Britain does manage to make a deal with the EU, the accord is likely to be partial or transitional.

A full deal for the future relationship will probably take years — up to seven years according to Tusk, or even a decade, according to reported comments by Britain’s former ambassador to the EU.