BRUSSELS (Reuters) - The European Union’s chief negotiator set a target of agreeing a Brexit deal with Britain by October 2018, assuming London keeps a promise to formally launch the process of leaving the EU by the end of March.

Michel Barnier, Chief Negotiator for the Preparation and Conduct of the Negotiations with the United Kingdom under Article 50 of the Treaty on European Union, holds a news conference at the EU Commission headquarters in Brussels, Belgium, December 6, 2016. REUTERS/Francois Lenoir

Michel Barnier, at a news conference on Tuesday, said the two-year deadline for final withdrawal fixed in Article 50 of the EU treaty meant there would be less than 18 months for actual negotiations.

British Prime Minister Theresa May has said she will give formal notification of Britain’s departure in March. Once a deal is struck, Barnier said, it will take some months to have it ratified by Britain, the other 27 states and the EU parliament.

“Time is short,” he said. “Should the UK notify the European Council by the end of March 2017 ... it is safe to say negotiations could start a few weeks later and an Article 50 agreement reached by October 2018.”

May’s spokesman said she was not expecting to negotiate for longer - something that would be possible only by mutual consent. If no deal is struck, Britain would simply be out of the EU but with possibly many complex legal loose ends left hanging.

“There is a two-year time frame,” the spokesman said after Barnier’s remarks. “We are not seeking to extend that process.”

British Foreign Secretary Boris Johnson said it was “ample” time. “With a fair wind and everybody acting in a positive and compromising mood, and I am sure they will, we can get a great deal for the UK and for the rest of Europe within that time frame,” Johnson told reporters on the sidelines of a meeting of NATO foreign ministers in Brussels on Tuesday.

Barnier said it was too early to say whether and how any transition period might be agreed after Brexit to allow time for negotiations on a future UK-EU relationship. That would depend on what Britain wants in future and what the EU would accept.

“NO CHERRY-PICKING”

He declined to go into what kind of relationship would be possible, though he cited the example of Norway, which accepts free migration and pays the EU in return for access to EU markets.

Asked about measures for the UK-EU land border that would be created across the island of Ireland, he said he would try not to harm the 1998 accord that brought peace to Northern Ireland.

Barnier cited four principles for negotiations: the 27 would be united; no negotiations before Britain’s notification; Brexit could not be a better deal than staying in the EU; and London could not keep full market access while keeping out immigrants.

“Cherry picking is not an option,” he said.

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Ramming home that message, the EU’s dominant leader, German Chancellor Angela Merkel, echoed his language to cheers from her conservative supporters at a party conference: “We will not allow any cherry picking,” she said in Essen, on the Ruhr.

“The four basic freedoms must be safeguarded - freedom of movement for people, goods, services and financial market products. Only then can there be access to the single market.”

Asked about debate in Britain over whether to seek a “hard” or “soft” Brexit, depending on how much market access to retain, Barnier said: “Frankly, I do not know what a hard or a soft Brexit are ... I can say what a Brexit is: ... We want a clear agreement; we want to reach this agreement in the limited time available; we want it to take account of our point of view.”

Barnier, a former French minister who irked many in London when he was the EU financial services commissioner, opened with a joke referring to speculation about his English language skills and his preference for holding negotiations in French.

“English or French?” he asked as he took the podium. He used both, though answered questions mainly in French. He also ventured a pop culture reference in English, summing up his message to London as: “Keep calm and negotiate.”