This is the “safeguarding” principle, common in international treaties, which David Cameron asked for in his pitiful attempt at a “renegotiation” last February; and which was inevitably refused because it is not open to members of the EU. But it is available to members of the EEA outside the EU, who can unilaterally claim it without any need for negotiation; as, for different purposes, both Lichtenstein and Iceland have demonstrated.

So obsessed are our Brexiteers with their wishful-thinking alternatives to remaining in the single market – each as unworkable as the rest – that they are determined to close their eyes to the one solution which, to a great extent, could enable us both to have our cake and eat it. If they got their way we would not only lose the cake but be left with nothing to eat in return.

That is the riddle Theresa May and her more sensible advisers need to confront before invoking Article 50, to trigger negotiations unlikely to begin until after Germany and France have held next year’s crucial elections. Meanwhile the EU itself stumbles blindly forward into the dark, without any clearer idea of how to solve the ever more pressing problem of its own future than President Juncker was able to offer last Wednesday.