BRUSSELS (Reuters) - European Union leaders will tell Prime Minister Theresa May next week how much longer Britain can stay in the bloc as British lawmakers struggle to agree on how and when, or even if, the country is leaving.

FILE PHOTO: Members of the European Parliament take part in a voting session in Strasbourg, France, March 14, 2019. REUTERS/Vincent Kessler

EU leaders meet for a two-day summit starting on Thursday, with many in two minds about how long Britain should get beyond the March 29 Brexit day, which is enshrined in law.

May, meanwhile, will ask the British parliament to back the deal she has negotiated with the EU for a third time, after it was twice roundly rejected.

These are the broad choices facing the EU, which must find a unanimous decision that May must agree with:

SLING THEM OUT NOW - MARCH 29

Britain is due to leave in 14 days at the expiry of a two- year negotiating period launched by May. She has said she will ask to extend that to June 30 if her deal is approved next week, to give time for legislation. Despite frustration with London, EU leaders have indicated they would accept a “technical extension” of a few weeks if a deal is in the bag. But if there seems little sign the stalemate is ending, some may argue it is better to end uncertainty for business and go to a “no deal” Brexit, for which they have prepared.

JUST A FEW WEEKS MORE - MAY 10-22

Few want to be blamed for forcing Britain out against its will. But Europeans vote for a new European Parliament from May 23 to 26. Many leading figures have said Britain must be out before then to avoid any legal challenge to the legislature’s legitimacy. The European Commission has said Britain must either leave by then or elect its own Members of the European Parliament (MEPs).

OUT BEFORE PARLIAMENT SITS - JUNE 30

This is the date May has given for an exit under her deal. The EU might accept a delay beyond the elections as the new parliament does not convene until July 2. As long as Britain were out by then, the lack of British MEPs should not pose a major legal problem.

The key question for any 2-3 month extension is will it resolve anything? The EU rules out reworking the deal May accepted. If she looks like she cannot ratify it, then a delay may give governments and businesses more time to prepare for a disruptive exit but leaders may also prefer to end doubts.

A short extension followed by a decision to extend for longer is possible in theory but senior EU officials say leaders will want a one-off delay.

GO AWAY AND THINK AGAIN - ANOTHER YEAR OR TWO?

May has said if she fails next week, she will seek a longer extension to reconsider the position. Summit chair Donald Tusk is urging the other 27 leaders not to rule that out. Some others back that line, though it may for now be a tactical choice to pressure hardline euroskeptics to accept May’s deal rather than risk a delay that might end up with no Brexit at all.

If May arrives at the Brussels summit deal-less, Tusk will argue that a short delay will achieve little but prolong uncertainty and, to avoid a disruptive no-deal, Britain should be asked to go away and sort out what it really wants - giving time for a new election or second Brexit referendum.

Some have suggested an extension to the end of this year, some for one year or to the end of 2020 or two years. It is not legally possible to leave it open-ended, EU officials say.

Advantages include: avoiding no-deal chaos, at least for now; keeping British funding for the EU for longer, although that would also continue in a transition period if the deal goes through; and potentially keeping the 28-nation EU together.

Disadvantages include: Britain having to return MEPs, disrupting a redistribution of seats in the European Parliament; a lopsided impact on parties, with the EU’s center-left gaining on the center-right and a boost for euroskeptic groups; prolonged uncertainty when the EU has other priorities; and the prospect of a lukewarm Britain staying when some would rather it left.