The main reason why the Brexit debate has gone round in circles for the last two years—and why the U.K.’s negotiations with the European Union have been almost completely stalled for months—is that much of the British political class have never fully understood what the EU is or how it works. The few who have evidently consider the implications so unpalatable that they dare not spell them out publicly.

How else to explain why with just eight months until exit day, the two main political parties remain officially committed...