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How should we measure success or failure for the government at the European summit?

David Cameron is no longer promising to use the talks to begin the process of restoring national control over some social and employment laws.

Instead, the prime minister has promised to secure protection for the City of London against any new EU regulation of the financial services' markets.

Judged against that aim, here's a ready reckoner guide to some possible outcomes of the late night negotiations:

EU agrees a good deal to safeguard the future of the euro by fixing tough new rules to prevent countries borrowing too much. Markets calm down and THE European Central Bank says it will start supporting Greece and other debt-ridden economies. David Cameron secures an explicit commitment from the EU for a new "emergency brake" that would allow the UK to veto any future financial services regulations that it does not like. Commitment to be included in the text of the newly tweaked treaties and thus legally binding.

EU agrees outline deal in principle for a new euro group fiscal union but many details still unclear. David Cameron secures language in the new treaty including a specific promise from the EU that any further integration of the eurozone would not damage the UK's financial services' market. Eurozone agrees to allow the ten non-euro countries to sit in on their meetings and promises to leave single market issues to the EU.

The 27 EU countries are unable to agree to treaty changes that would allow for closer integration of the eurozone. The 17 eurozone countries promise to agree a new treaty among themselves. As such, the UK would not be able to insert any protection for the City of London in the new treaty. But the summit communique promises that the eurozone would not do anything to undermine the single market in financial services.

Neither the EU nor the eurogroup agree to an explicit deal on further integration of the eurozone but sign up to some broad principles which will be taken to another summit next week. David Cameron secures some non-legally binding language in the text of the summit communique in which the EU promises to do nothing to undermine the single market. UK officials insist that this is an implicit reference to protecting financial services and the City of London.

No deal on the euro as France and Germany fall out over how tough and legally binding the new rules must be. David Cameron fails to secure any allies in the negotiations and fails to win any new protection for the City of London against existing proposals for new financial regulation. Summit breaks up as markets plummet.