European leaders say 26 out of 27 EU member states have backed a tax and budget pact to tackle the eurozone debt crisis.
Only the UK has said it will not join. Prime Minister David Cameron said he has to protect key British interests, including its financial markets.
The UK effectively used its veto to block an attempt, led by the French and Germans, to get all 27 EU states to support changes to the union's treaties.
Instead, eurozone members and others will adopt an accord with penalties for breaking deficit rules. It will be backed by a treaty between governments, not an EU treaty.
German Chancellor Angela Merkel said the UK was the only country to have expressed reservations, but that Mr Cameron had recognised that a stable euro was in Britain's interest.
Of the nine other EU countries outside the euro, Hungary, the Czech Republic and Sweden have said they must consult their parliaments. Six others - including Denmark, Poland and Latvia - have agreed to join the new deal.
However, some countries - such as the Republic of Ireland, which is in the eurozone - have a constitutional requirement to hold a referendum on any major transfer of powers to the EU.
EU leaders aim to have the pact - known as a "fiscal compact" - ready to take effect by March.