Factbox - X+Y+Z equals? UK-EU deal boils down to summit semantics

By Alastair Macdonald BRUSSELS (Reuters) - When British Prime Minister David Cameron meets fellow EU leaders in Brussels in a week, they will argue over stubborn differences on a broadly agreed text on EU reform to help keep Britain in the bloc. It is unclear how far any accord may do more than provide domestic political comfort for Cameron to campaign to retain British EU membership in a referendum. But whether a summit deal is struck will come down partly to semantics, partly to filling in blanks in a draft that limits a new mechanism for curbing immigration to a period of "[X] years ... plus [Y] plus [Z]". The following will be key areas for debate: EURO ZONE One of only two EU states neither to use the euro nor be bound to adopt it in time, Britain stands alone in insisting there will never be just one currency in the bloc, and Cameron demanded safeguards, particularly for London's vital financial sector, from being harmed by decisions taken by the euro zone. An initial draft secured assurances to that effect but raised concern in France that different banking regulations in London and the euro zone could unfairly benefit the former. The new draft introduces wording to strengthen the need for rules to be uniform among states inside and outside the EU banking union. NATIONAL SOVEREIGNTY Cameron has secured a repeat of an EU assurance that treaty commitments to an "ever closer union" of the peoples of Europe are not "equivalent to the objective of political integration". But in a nod to federalists, including Belgium and France, the amended draft says that, nonetheless, political integration "enjoys wide support in the Union". In assuring Britain that EU states retain sole responsibility for their national security, it adds: "The benefits of collective action on issues that affect the security of all member states is recognised." TREATY CHANGE Ensuring that reforms are legally binding and amount to a lasting change in the EU treaties has become a touchstone of domestic credibility for Cameron. Passages of the draft text saying that EU leaders agree to incorporate "the substance" of their agreements on the euro zone and sovereignty into EU treaties when next they come up for amendment remain in doubt. EU officials say that an agreement among leaders at the summit will constitute a binding inter government treaty and so a pledge to treaty change may be unnecessary. Many governments fear that a mounting euroscepticism across Europe will make it very difficult to win popular ratification for new EU treaties. MIGRATION Long seen as the trickiest of the British demands, the EU offered an "emergency brake" mechanism to help Cameron fulfil promises to reduce immigration from the EU by curbing welfare benefits to EU workers for up to four years after they arrive. Most governments have accepted that extraordinary circumstances give Britain the right to apply this "brake". But Poland and its eastern allies want to limit to four years the period Britain can penalise their citizens. The text sets a maximum of four years during which an individual can be denied benefits. But it refers to the total period that a state can exercise the emergency brake only as "[X] years, extendable for two successive periods of [Y] years and [Z] years". Britain would like that to add up to at least seven - equal to the period it did not exercise its EU right to bar Eastern European workers after they joined the EU in 2004. That early British welcome to workers from the ex-Communist east appears in the new draft, which says a right to use the emergency brake is mainly intended for countries that did not bar new members' citizens for a transition period. That wording aims to reassure those worried that states other than Britain may try to use it. Cameron also faces questions from easterners on how far he will try to cut child allowances for workers in Britain whose children live in poorer states by indexing them to living costs. (Editing by Peter Cooney)