In 1955 a Conservative government led by Anthony Eden took the catastrophic decision of opting out of the European Community at its inception, impulsively and without really thinking about it. Britain then spent years desperately trying to join in the face of repeated rebuffs and eventually gained admission only in 1972. By that time it was too late to influence the shape that Europe took and we have felt an uncomfortable member of it ever since.

Fifty-six years later, another Conservative government has made another catastrophic decision to opt out of a treaty that will shape Europe over the next several decades, without really thinking about the consequences. The alliance of the nine other “outs” we were counting on to stand with us in a quasi-European Free Trade Association evaporated within hours. As after 1955, we will now have to spend decades trying to join something we should have joined in the first place. And Europe will suffer from the absence of a strong economically liberal voice moderating the statist tendencies in many of the other member states.

As we found out in Tony Blair’s government, crucial decisions like this can slip past you without you fully being aware how crucial they are. What happened on Friday became the defining moment of this premiership without David Cameron even recognising it was happening.