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The cheers as David Cameron walked into the House of Commons said it all.

Conservative MPs liked what they heard today. Not just the promise of a straightforward in/out referendum, not just the pledge to renegotiate Britain's relationship with Europe but also an apparently esoteric commitment to challenge the EU's founding principle - to "ever closer union".

Their joy was increased when Ed Miliband made clear - or rather seemed to make it clear - that he was opposed to any such referendum. Those Tory smiles increased yet further when Labour spindoctors insisted that "NO" didn't mean "No" to any referendum ever whatever the circumstances - just a promise of this one made now.

Job done then for the prime minister? Oh no. Now he will face eurosceptic calls to spell out exactly which powers he wants to wrestle back from Brussels and demands to be tougher. He'll be pushed again and again to explain in what - if any - circumstances he might declare that any new deal with Europe was not enough and Britain should leave. If, as today, he refuses he'll be told his is a weak negotiating hand. He will be leading a party who feel that they've been given permission to - in words David Cameron used when he became their leader - "obsess about Europe" again.

And after that there's the small matter of finding out if any one of Europe's 26 other leaders will actually give him what he wants when he wants.

Welcome to page one of the latest chapter in the longest running and bloodiest saga in British politics.