As the start of Brexit negotiations with the EU-27 looms, the trickiest conundrum facing Theresa May is that of reconciling the need to agree continuing access to the single market for British business with her insistence on ending UK participation in EU free movement.

Taken at face value, it is impossible to resolve. EU leaders have been consistently clear that Britain cannot have access to the single market without accepting free movement. If restoring control of our borders is so important, we will have to make do with a free trade deal from outside the single market – like the ones Canada or South Korea negotiated (after 8 and 7 years of discussions respectively).

But Theresa May thinks she has found a third way: a sector-by-sector approach. Her plan is for the UK to leave the single market en bloc, but renegotiate continued access to it on preferential terms for some key UK industrial sectors as part of a wider free trade agreement. According to this vision, these lucky sectors would continue to enjoy de facto membership of the single market, but without the requirement to be bound by decisions of the European Court of Justice. Problem solved, our Prime Minister thinks. We get our borders back, we ditch the ECJ’s jurisdiction, and the sectors most dependent on the European market continue to operate inside the single market, without the bits we don’t like. Simples.