(The author is a Reuters Breakingviews columnist. The opinions expressed are his own. Refiles to add dropped word "billion" in second paragraph and correct formatting/style.)

LONDON - Brexit is rapidly becoming a symbol without substance. Prime Minister Theresa May’s last-minute deal with the European Union reduces the chances of a chaotic divorce but exposes the difficulty of preserving trade flows after the separation. A lengthy transition period will create further scope for May – or another prime minister – to make concessions.

The first phase of Brexit talks was supposed to be straightforward. In reality, the six-month negotiation was punctuated by British compromises. Despite initial protestations, the government will pay a divorce bill that UK officials estimate will be between 40 billion and 45 billion euros. It also conceded that the European Court of Justice can rule on disputes involving EU citizens for up to eight years after Britain leaves.

The biggest climbdown, however, was over the border with the Republic of Ireland. Ministers had insisted it was possible to leave the EU’s single market and customs union without reintroducing a hard border. That was exposed as naive. Decisions on a detailed plan are deferred to the next stage of the talks. In the absence of a solution, however, the UK has committed to maintaining “full alignment” with the EU rules required to keep the border open.

The tussle is a preview of the issue likely to dominate the next phase of the talks: Britain’s willingness to comply with EU regulations after quitting the bloc. May wants an ambitious pact, but also insists on her country’s right to determine its own future. Officials in Brussels say that means London may have to settle for an agreement like the one the EU has with Canada. Even that could prove tricky since all 27 remaining EU nations will have to approve it.

Fully resolving this question by March 2019, when Britain is due to leave, looks impossible. A transition period, initially of two years, will buy time to agree details. Once in place, that limbo could easily be extended. May might then make further concessions – or be replaced by a prime minister not bound by the same “red lines”. Reversing the referendum decision still looks unlikely. But the chances of Britain leaving the EU in name only will continue to grow.

CONTEXT NEWS

- Britain and the European Union on Dec. 8 agreed the outline of their divorce, clearing the way for talks about trade and a transition period.

- The European Commission said enough progress had been made after the two sides worked through the night to end an impasse over the status of the Irish border that had scuppered an earlier attempt to clinch a deal.

- Donald Tusk, the chairman of European Union leaders, welcomed the deal but said Britain still needed to provide more clarity on the new relationship after Brexit.

- A joint report from negotiators spelt out the agreement on the rights of EU and UK citizens after Brexit, the terms of the financial settlement, and the status of Northern Ireland.

- The report said Britain intended to avoid a hard border in Northern Ireland through the broader relationship between the two. In the absence of a deal, Britain would propose “specific solutions” to avoid a hard border, and in the absence of any such solutions would “maintain full alignment” with rules of the EU Single Market and Customs Union which support North-South agreement.

- The commission will now begin work on the next phase of talks, which cover a transitional period, trade, and long-term relations with the bloc. Draft guidelines showed the transition period would last around two years. During that time, Britain will remain part of the customs union and single market but will no longer take part in EU institutions or have a vote. It will still be subject to EU law.

- By 0900 GMT the pound was trading at $1.3488, up 0.1 percent, and at 1.148 euros, up 0.35 percent.

(Reporting by Peter Thal Larsen; editing by Swaha Pattanaik and Martin Langfield)

© Reuters News 2017