Factbox - EU's Tusk offers reform package to Britain's Cameron

BRUSSELS (Reuters) - The head of the European Council, Donald Tusk, unveiled on Tuesday a draft reform package to help keep Britain in the EU following meetings between Prime Minister David Cameron and top EU officials. The following are key points of the proposal that will be discussed by EU envoys on Friday and which could form the basis of a deal with Britain at a summit on Feb 18-19. STARTING POINT The proposal is just the starting point for negotiations, which top officials expect will last until the very last minute. In anticipation of difficulties, no time limit has been set for the talks on the second day of the EU summit on Feb. 19. Nothing is agreed until everything is. A deal, needing all 28 national leaders' assent, could pave the way for a referendum as early as June. An impasse would probably spell more talks. The EU sees its proposals as legally watertight, safe from challenges in court and not requiring amendments to treaties now - something hard to pull off quickly across all 28 EU states. On some issues, Tusk has raised the possibility of the treaties being amended later to incorporate the substance, if not the exact language, of the proposals unveiled on Tuesday. MIGRATION Cameron wants to discourage other Europeans from coming to Britain by excluding them from the tax credits, child allowances and other non-contributory social benefits attached to low-paid British jobs for at least four years. Without changing EU treaties guaranteeing free movement of labour and barring national discrimination, the EU proposed an "emergency brake", limiting those fundamental rights where vital national interests or economic stability are at risk. Legislation to be drawn up by the European Commission is to give any state the right to curb in-work benefits for up to four years. This would hinge on the consent of a qualified majority of other European governments if there is an exceptional inflow of workers from elsewhere in the EU. Allowances for children that EU migrant workers send back to their home countries are to be indexed with purchasing power parity. This would effectively make payouts for children smaller in poorer member states such as Poland. EURO ZONE Cameron wants more legal safeguards for Britain's sterling-based economy and big financial industry from a risk of the euro zone countries writing EU rules to suit them. The EU said on Tuesday that no British company or citizen would face discrimination because they use the pound as a currency -- a safeguard for the City of London that it will not be left outside any EU financial projects because Britain is not, and does not plan to become, a member of the euro zone. The EU is also offering Britain a way to slow down euro zone legislation that it does not like, although it is careful not to offer London any veto rights on euro zone decision-making. NATIONAL SOVEREIGNTY Cameron wants assurances that Britain need not hand more power to Brussels and to enhance the say of nation states within the EU. The Tusk package explicitly states: "It is recognised that the United Kingdom, in the light of the specific situation it has under the Treaties, is not committed to further political integration into the European Union." The EU also offers to allow a simple majority of national parliaments - each of which has two votes, regardless of size - to stop legislative proposals from the Commission. COMPETITIVENESS The least contentious area of Cameron's four reform "baskets", calling for less red tape and more economic dynamism has broad backing so a set of declarations will echo EU policy, but with elements to show Britain that Brussels is listening. The Tusk package endorses all that. (Reporting by Paul Taylor and Alastair Macdonald; Writing by Alastair Macdonald and Jan Strupczewski; Editing by Gareth Jones)