European Union leaders will endorse a stiff set of divorce terms for Britain at a summit on Saturday, rejoicing in a rare show of unity in adversity, but well aware that may start to fray once negotiations begin.

Meeting for the first time since British Prime Minister Theresa May formally triggered a two-year countdown to Brexit in late March, the 27 other EU leaders will lose little time over a lunch in Brussels in approving an eight-page set of negotiating guidelines hammered out by their diplomats over the past month.

In a mark of how last year's Brexit vote has called into question the unity of the United Kingdom itself, leaders will also offer Irish Prime Minister Enda Kenny a pledge that if Northern Ireland, which voted against Brexit, ever unites with his country, it will automatically be in the EU.

The leaders may spend more time in discussions, including with European Chief Negotiator for Brexit Michel Barnier, on what criteria they may use to judge, come the autumn, whether he has made sufficient progress to warrant a start on trade talks. They may also talk about how to manage a transition, after Britain leaves in 2019, to a new relationship likely to take many more years to finalize.

That decision on what is "sufficient" is the kind of debate that can poison relations as the 27 members seek to protect national interests. Also contentious will be which countries scoop the prizes of hosting two EU agencies set to be moved from London.

With most of the 27 offering to house the European Medicines Agency (EMA) and several wanting the European Banking Authority (EBA), summit chair Donald Tusk and EU chief executive Jean-Claude Juncker will propose they agree in June on criteria for making the choices to avoid a repeat of previous bunfights.

"We are remarkably united," one national leader who will be at the table told Reuters this week. "But then it's always easy to be united on what you want before you start negotiating."

(Source: Reuters)