Some of the very best and some of the very worst ideas command unanimity. As everyone agrees that Britain’s pro-Europeans must help make the most of an EU exit, should we nod along at the common sense – or worry?

Even heartbroken Remainers are sure of the case for constructive engagement. The morality and tactics seem unanswerable. There is something of the prima donna, not to say the national traitor, in the act of abstention, as though the country was only ever worth a damn as long as it voted for Europe.

If Remainers team up with liberal Leavers, they can brainstorm a model of exit that minimises disruption and maximises Britain’s economic openness.

Theresa May can be bullheaded but she is not a sadist: if the expected loss of single market membership chills economic sentiment, the prime minister will think before signing off on such a deal. Remainers can bring their influence to bear or, like Lucifer, plead non serviam. The dilemma seems to be no dilemma at all.

Except, it is. Sometimes history throws up ideas that are better tested than forever stymied. Britain’s mastery of its own affairs, even at the cost of access to the European market and the political chambers that regulate it, is a big, legitimate idea that has stirred politics for 30 years. If it is not allowed to run its course, even after a referendum in its favour, it will not disappear – it will intensify in the shadows and return in more fearsome form.

This is not just about future troubles but immediate ones, too. Referendum mandates can be opaque, but June’s sent one intelligible signal: the end of free movement is, for the public, a non-negotiable demand. The European single market, even when accessed on the lesser Swiss-Norwegian terms, is conditional on free movement. So, unless they believe the EU or the British electorate is bluffing, Remainers (and the most tentative Leavers) are not much use in the process of withdrawal. The only exit is hard exit.

Bad options

That argument, to stress, ultimately rests on the principle that ideas, unless they are plainly malign or ruinous, have to be held accountable in the end by real-world application. There is only so much mileage in the statecraft of frustrating them, especially when elite collusion (real and imagined) already incenses people.

If exit is neutered by the referendum’s losers before it even gets going, you can script the Eurosceptic reaction. For a certain kind of lefty, socialism has never failed in real time and space. It has only been implemented halfheartedly by running dogs and revisionists. A minority of people who voted Leave think like this.

Most are practical types who knew they were taking a punt. They are open to the falsification of their project. But a softened exit would entitle both kinds of Leaver to disown whatever happens in the coming years. Every sentence would start with “If only . . .” If only true believers had led the government. If only Brexit had meant Brexit.

Eurosceptic id

Events must take their course, and this view is not offered with any relish. The proposition that the Labour Party can win from the hard left probably had to be tested at some point, but the process of discovery may reduce the official opposition to debris.

A clean break from the EU would involve economic disruption and some permanent losers. Even if it does not, no conscientious person could be relaxed in finding out.

This reality must be weighed against others, though. There is the lack of options: the small scope for a mitigated exit. There is the danger of populists having another betrayal story to tell. There is the fact, lost in the hubbub, that exit is as reversible as entry turned out to be. Britain might leave the single market, find life invidious and gradually creep its way back in through ad hoc deals with the EU that pile up over time. If Britain stays out forever, then by definition the costs will be bearable.

It is impossible to know what will happen after a hard exit but almost as impossible to see an alternative to finding out. Pro-Europeans must show goodwill during the process, but probably from the margins. – Copyright The Financial Times Limited 2016