"Time will be short," the EU's chief Brexit negotiator Michel Barnier said at a news conference in Brussels on Tuesday. "All in all, there will be less than 18 months to negotiate.

"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," Barnier added.

UK Prime Minister Theresa May has said she plans to invoke Article 50 of the EU treaty by the end of March 2017, formally triggering a two-year deadline to withdraw from the bloc.

However, Barnier warned that the effective negotiating time will be less than that as it will take some months for the deal to be ratified by Britain, the other 27 EU member states and the European Parliament.

While declining to anticipate what kind of Brexit deal the UK could secure, Barnier dampened talk that the UK could "cherry-pick" to keep what it likes about the EU. Single market access and its "four freedoms" - the free movement of goods, services, capital and labor - are "indivisible" he said.

That messaged was reinforced by German Chancellor Angela Merkel at the Christian Democratic party conference in Essen on Tuesday to cheers from her conservative supporters. "We will not allow any cherry picking," she said.

Barnier also cited four principles for the negotiations: the 27 member states would remain united; there would be no negotiations before the UK triggered Article 50; Brexit could not be a better deal than staying in the EU; and the UK could not keep full market access while refusing to take in immigrants.

"This will be the atmosphere in which we will be conducting our negotiations with the UK and the sooner the better," he said. "We are ready; keep calm and negotiate."

Asked about debate in Britain on how much market access the country will retain - coined as a "hard" or "soft" Brexit - 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."

UK undaunted by deadline

A spokesman for May said the prime minister was not expecting the negotiations to take longer.

"There is a two-year time frame," the spokesman said following Barnier's remarks. "We are not seeking to extend that process."

Speaking to reporters on the sidelines ahead of a NATO meeting of foreign ministers, British Foreign Secretary Boris Johnson appeared unconcerned by such a deadline, saying 18 months 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," he said.

However, May's plans could be delayed if the British Parliament needs to give it approval before the government can trigger Article 50, as a British court ruled last month. The government is currently contesting the ruling in the Supreme Court. A lawyer for the British government warned on Tuesday that the Supreme Court would fall into a "serious constitutional trap" if it upholds the ruling.

May accepts calls to publish Brexit plans

The UK government has so far remained reluctant to reveal what kind of post-Brexit relationship it wants with the EU, out of fear it could weaken its negotiating position. 

On Tuesday, however, May indicated that she would publish her Brexit plan before launching formal exit talks. The decision stems a rebellion by up to pro-EU 40 lawmakers from within her own party as to whether she should set out her plans before triggering Article 50.

A motion was raised by the opposition Labour party to pressure May to reveal her hand ahead of exit talks. Labour's motion "calls on the prime minister to commit to publishing the government's plan for leaving the EU before Article 50 is invoked." However, it also "confirms that there should be no disclosure of material that could be reasonably judged to damage the UK in any negotiations."

In its revised amendment published on Tuesday, the government said it will accept the demand, while in return asking that parliament respects the Prime Minister's Brexit timetable.

On Tuesday evening, the Conservative parliamentarian Steve Baker tweeted the government's amendment.

After repeatedly refusing to outline its Brexit negotiating strategy, a government spokeswoman denied that the amend signalled a U-turn. "We have always said we would come forth with more detail as we near the moment of triggering Article 50," she said.

The motion, however, is not binding and if not enough parliamentarians voice their agreement, it may not even necessitate a formal vote.

dm/se (AP, Reuters)