By Alastair Macdonald
BRUSSELS (Reuters) - European Union leaders will set out plans this week for negotiating Britain's exit, diplomats said, after national officials met late on Monday to prepare an EU summit statement.
After the 28 national leaders meet in Brussels on Thursday, British Prime Minister Theresa May will leave and the other 27 will dine without her and agree principles on how negotiations with London will be run once May formally launches the process.
Building on a first statement made by the 27 in the week after Britain's June 23 Brexit referendum, they will clarify that Britain remains a full member until it leaves the EU but will also note that it will be excluded from various forums of the Union which will be involved in negotiating divorce terms.
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The statement will not go into the substance of terms that Britain might be given, including on the status of expatriates living on opposite sides of a new UK-EU border, despite calls from Britain for the Union to offer them immediate assurances.
The leaders will remind May that they want her to trigger the two-year withdrawal process as soon as possible; she says she will do so by late March, although judicial wrangling in London could still delay that. And they will reiterate that they will not negotiate with her until May sets the clock ticking.
EU officials say it will take the Union some six weeks to formally respond with a negotiating mandate for the executive European Commission -- a period that in itself may be affected by France's two-round presidential election in April and May.
As is normal in EU diplomacy, the Commission -- in this instance led by its chief Brexit negotiator Michel Barnier -- will handle the detailed talks. But unlike most international discussions by the Union, member states will be represented in much of the process by officials reporting back to the 27.
This is a particular concern for smaller states, officials say, as they have less confidence than major powers like France, Germany and Italy in their ability to influence the Commission.
Diplomats from the 27 stress they are united and determined not to let Britain benefit from dividing them to cut a better deal in Europe than it has had as an EU member. However, they also have different interests which London could try to exploit.
(Editing by Jonathan Oatis)