Britain is not leaving the European Union, just yet. But the EU may already have abandoned Britain. The fog of the Battle of Brussels, 8-9 December 2011, is still clearing. But psychologically and politically a Rubicon has been crossed, both in Brussels and in London.

The Prime Minister has played a poor hand very badly. He has put Britain into a position of deep isolation within the EU which even Mrs Thatcher in her "money-back" days skilfully avoided. He has given the circling sharks of the Eurosceptic backbenchers and press a taste of blood which could rapidly turn into a feeding frenzy.

Months of difficult negotiations lie ahead in which Britain will find itself willingly cast as the villain by our anxious European partners as they struggle to avoid the collapse of the euro. In such a febrile mood, in Britain and on the Continent, the possibility of a de facto, or even actual, UK departure from the EU is no longer unthinkable.

Past EU-UK battles have been about important but fundamentally secondary issues, such as farm policy or budget contributions or "mad-cow" beef exports. Mr Cameron has managed to manoeuvre himself into a position of Britain vs the Rest on the most fundamental issues of all: the survival of the euro and the EU itself.

The Prime Minister was presented in the European media yesterday as a kind of wicked fairy. He did not want to go to the proposed, new euro-27 treaty ball. That was his right. But to please his party's Eurosceptics, he refused to allow the others to hold the ball unless they gave Britain, or rather the City of London, an "unwedding" present.