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"What I say is what I do."

That is what David Cameron says you can learn from his decision to force a vote at this EU Summit - a vote which he looks certain to lose and lose big. This is, he told me hours before 28 EU leaders meet for dinner in Ypres, just the "start of a long campaign".

It is a message directed as much at voters back home as fellow European leaders. It's meant to say: "I will not compromise on my principles, I will not do last minute deals, I will not back down even when facing isolation".

Many Tory voters who've defected to UKIP tell pollsters that they don't trust David Cameron to hold a referendum let alone to get a better deal for Britain in Europe. After all, they say, doesn't the prime minister keep telling people that he really wants to stay in the EU?

Although this is a crisis he didn't expect - and didn't want - the prime minister is now using it to try to win credibility with those Cameron-sceptics.

What will be fascinating is to see whether he takes the next logical step. Many sceptics argue that the complete failure of his negotiating strategy proves that you can never win in Europe whilst everyone believes you are determined to stay. So, might David Cameron be tempted to take the next step which he has so far resisted by declaring that if the EU will not reform in the way he wants he would be unable to recommend that Britain should stay in?

It would be a public version of what Germany's Angela Merkel called his private threat that Britain would be more likely to leave if Mr Juncker is chosen as the next President of the European Commission.

It would be a huge diplomatic and a political gamble. Other European leaders could react by treating Britain as if she is already heading for the exit. Some businesses may reconsider their investments in the UK. It would seem, however, to be the logical conclusion of the Tory leader's "what I say is what I do" rhetoric here.