ConservativeHome’s Tim Montgomerie says the Lisbon Treaty Referendum is off.   Guido has dug out the September 2007 text of Cameron’s famous cast-iron guarantee to Sun readers.

The final reason we must have a vote is trust. Gordon Brown talks about “new” politics.  But there’s nothing “new” about breaking your promises to the British public. It’s classic Labour. And it is the cancer that is eating away at trust in politics.  Small wonder that so many people don’t believe a word politicians ever say if they break their promises so casually.  If you really want to signal you’re a break from the past, Prime Minister, do the right thing – give the people the referendum you promised.

Today, I will give this cast-iron guarantee: If I become PM a Conservative government will hold a referendum on any EU treaty that emerges from these negotiations.  No treaty should be ratified without consulting the British people in a referendum.

If it is ratified what is the meaning of this promise?  The Tories will stand on a Eurosceptic ticket and they will be in government with a treaty that has not been sanctioned by a referendum.  Unless they turn the election itself into a referendum, which is risky.  Only if the Tory manifesto says “we will renegotiate our relationship with the EU thus…” will they be able to say they have consulted with and won a mandate from the British people. Will Ken Clarke go along with that?

UPDATE : The Bruges Group headbangers have gone nuclear, Barry Legg has released a statement:

“There was absolutely no wriggle room in the unambiguous pledge he made in September 2007. He offered a “cast iron guarantee” to put any treaty in front of the voters. Why has he changed his mind now? What has changed his mind now?

“It cannot be good enough for a man who wants to be British Prime Minister to hide behind the leader of any other European state. Václav Klaus is a hero in his own country for having stood up to Communism. David Cameron seemingly can’t even stand up for his own past promises.

“What is the point in David Cameron upending one pledge on Europe , but promising he’ll offer us yet more European promises in his general election manifesto? Why will they be any more credible than the ‘cast-iron guarantee’ he has just broken?

“How can David Cameron claim he’ll fight to repatriate powers from Brussels when he won’t even fight to implement his own past words?