The outcome of the Brussels summit on December 8th and 9th is a disaster for the UK and also threatens the integrity of the single market. For more than 50 years, a fundamental principle of Britain’s foreign policy has been to be present when EU bodies take decisions, so that it can influence the outcome. David Cameron, the prime minister, has abandoned that policy. Britain will not take part in a new fiscal compact that most other EU countries will join.

France and Germany have persuaded the other eurozone countries that treaty changes are needed to enshrine stricter budget policies and closer economic policy co-ordination. The new procedures would apply only to countries in the euro. Most member-states wanted to enact those reforms through amending the existing EU treaties. That would ensure that countries in the euro, and those outside, would be subject to a single set of rules and institutions.

But Britain blocked that deal, pushing France, Germany and most other member-states to proceed with a new treaty, to sit alongside the EU treaties. The new treaty may face difficulties: the Irish may hold a referendum on it and could easily vote no. But Paris and Berlin are determined to press ahead with the fiscal compact and if the Irish vote against it they are likely to find themselves excluded.

Cameron blocked a treaty for all 27 because he could not obtain agreement on a protocol to protect the City of London. This protocol demanded a switch from majority voting to unanimous decision-making on a number of issues that matter for the City, including the extension of the powers of EU regulatory authorities, and rules that prevent national governments from imposing stricter requirements on bank capital.

Cameron was right to seek to protect the interests of Britain’s hugely important financial services industry. Most financial regulations are decided by qualified majority vote, and there is a risk that new EU rules could damage this vital national interest. However, Britain has never yet been outvoted on a significant piece of EU financial regulation. If Cameron had been prepared to compromise on his demands, he might have been able to secure a deal.

But France’s president, Nicolas Sarkozy, was annoyed by Britain’s demand for special treatment, and had no desire to do the City favours; indeed, after the summit he said that a lack of regulation of financial markets was responsible for many of the current problems. Other heads of government found Britain’s demands and the way it presented them unreasonable. They also complained about the lack of British diplomacy: the British Treasury took its time to draft the protocol and did not present it to the Council of Ministers legal service until the day before the summit. The British made no effort to sell the protocol to most of the member-states. In short, there was little goodwill towards Cameron.

As far as I can gather, the UK government’s position stiffened between the morning of December 7th and the evening of December 8th. At the start of that period, Cameron seemed to want a deal, as his article in The Times indicated. But then loud rumblings from Conservative eurosceptic backbenchers – and calls for a referendum from two cabinet ministers and London Mayor Boris Johnson – made the Conservative leadership reluctant to show flexibility. Some senior Conservatives worried that if the government accepted a new EU treaty it would struggle to push it through Parliament. Many Tories would have rebelled and it probably would have passed – if at all – only with Labour’s support, thereby humiliating Cameron. That is why some senior figures in the government did not want a deal in Brussels.

But Britain’s so-called veto – which has not stopped anything from happening – seems likely to damage its interests. For a start, the government failed to achieve any sort of protection for the City. The countries taking part in the new arrangements (between 23 and 26 member-states are likely to adopt them) will meet regularly and discuss economic policy. They are also bound to talk about single market issues such as financial regulation. In theory, single market matters will still be settled by all 27. In practice, the countries in the new club are likely to caucus and pre-determine the results of EU votes on single market rules – whether they concern the City or other matters.

In the new arrangements, the Commission and the European Court of Justice will almost certainly play a diminished role. That is because France and Germany, the dominant countries in the fiscal compact, are hostile to the Commission and favour a more ‘inter-governmental’ Europe. To the extent that these institutions are weaker, they will be less able to do their job of defending the single market and ensuring that all member-states are treated fairly.

Some British eurosceptics seem to imagine that the new club will not be allowed to use EU institutions without Britain’s permission. There are likely to be complicated law-suits, but if most member-states want the Commission and the Court to play a role in the fiscal compact, these institutions will play a role. The institutions will have to try and reconcile two sets of rules and procedures, which will make it harder for them to do their job of policing the market.

What if the eurozone countries want to harmonise banking regulations, which they may need to do in order to ensure the success of the euro? Britain would not support a centralised system of banking regulation, but could easily be outvoted. Rules on banking regulation, like other single market issues, will remain subject to qualified majority voting among the 27. But if Britain wants to win votes, it will need allies.

I can never recall Britain being so friendless in the EU. Countries that might be sympathetic to the UK, such as Denmark, the Netherlands, Poland and Sweden, have grown impatient with the Cameron government. They have always wanted Britain to be influential in Europe, to balance the power of France and Germany. They would have much preferred all 27 countries to stay together. Britain’s self-exclusion has left them disappointed. Many of the smaller member-states are unhappy: when EU institutions weaken, they are more likely to be pushed around by France and Germany.

Since it joined the EU in 1973, Britain’s impact on the EU has been positive in many ways. It has pushed for legislation to bring about the single market. Together with France, it invented EU defence policy and it has contributed a lot to EU external policies, in areas such as the Balkans, Iran and climate diplomacy. It has helped to maintain the EU’s Atlanticist orientation. It has encouraged the EU to look outwards and see globalisation more as an opportunity than as a threat. With Britain’s voice diminished, the EU is less likely to deepen the single market and more likely to be inward-looking.

It is conceivable that a different British government could seek to reverse this disastrous opt-out. More likely, Britain will continue on a path towards isolation, perhaps even leaving the EU itself.