Why not simply stay in the existing customs union for an interim period rather than try to create a new one? First that would mean staying in the EU longer, since only EU members can be in the EU customs union. Second, for legal reasons, that would preclude the International Trade Secretary, Liam Fox, from being able to negotiate new trade deals with the likes of America and New Zealand - and for some reason giving Fox something to do has also been judged by the Government to be an inviolable imperative stemming from the referendum result.

It is unknown whether the EU will accept the Government's interim customs proposal, but there are good reasons to suspect they will not. And, even if they did, the bigger problem is that a temporary new customs union in 2019 still isn't enough to avoid a cliff-edge for UK firms.

Even if the EU agrees to the transition and the UK and EU successfully recreate a new temporary union, there will still be major trade frictions. Turkey has a customs union with the EU but Turkish imports still have to be checked at the border to ensure compliance with EU standards. There are long queues of lorries at the Turkish-Bulgarian border.