"He's sold us down the river". So said one party leader of David Cameron's new EU stance. Except the leader in question wasn't Ukip's Nigel Farage but Ed Miliband, speaking on ITV's Daybreak this morning. The Labour leader has annexed the language of betrayal from the Conservative right. He went on: "I'm going to be asking him in the House of Commons today what exactly has he agreed to, what protections has he got for Britain." Do his words, combined with the threat to vote against additional UK funds for the IMF, herald the long-awaited rebirth of Labour euroscepticism?

Whatever the answer turns out to be, it's not hard to see why Miliband is keen to maximise Cameron's political discomfort. The Prime Minister will return from Brussels today to a Conservative revolt over his decision to allow EU countries to use the European Commission and the European Court of Justice to enforce their new "fiscal compact". The Prime Minister's "veto", you'll recall, was supposed to prevent just such an outcome. The government continues to warn of legal action if Britain's interests are "threatened" by the new treaty (in other words, that the single market is undermined) but it's still a U-turn by any measure.

So, what explains this outbreak of pragmatism? In a phrase, Cameron has put economics before politics. The priority, he insists, is to resolve the eurozone crisis by ensuring the swift implementation of the new treaty. It's hard to see how the pact, committing EU members to German-style austerity, will aid European recovery but Cameron's intentions, at least, are good. As the PM commented yesterday:

The key point here for me is what is in our national interest, which is for them to get on and sort out the mess that is the euro. That's in our national interest.

But his backbenchers, many of whom are appalled that the UK is collaborating in the establishment of a fiscal union, don't accept Cameron's logic. The PM's willingness to allow the EU 25 (everyone except the UK and the Czech Republic) to use EU-wide institutions renders his veto meaningless, they argue. Here's Tory MP Douglas Carswell:

I don't see how the veto is really a veto if we allow the fiscal union members to form and to then find ourselves subject to the EU institutions being used to govern that.

With 20 MPs reportedly meeting in Edward Leigh's office last night, we can except plenty of dissenting voices when Cameron delivers his statement on the summit at 3:30pm in the Commons. But what the revolt currently lacks is a frontbencher, Iain Duncan Smith, say, or Owen Paterson, to tighten the noose on the Prime Minister. Until such a figure publicly intervenes, Cameron will probably be able to muddle through. But less than two months on from his celebrated "veto", the truce he struck with his MPs is under increasing strain.