Charles Michel, the federalist Belgian prime minister, sought to halt any ratcheting of British demands last week by inserting a self-destruction clause in Mr Cameron’s deal, stating that the offer of an emergency brake on migration and a red card system for parliaments would evaporate in the event of a No vote, forcing any future negotiation to start from scratch. Given the lukewarm reception for Mr Cameron's deal this weekend, they may have to think of something stronger.