I have long accepted, unlike many Brexit-backing economists, the need for a transition period after the UK formally leaves the EU.

After over four decades of membership, extracting ourselves is a complex process. British businesses, not least our exporters, need time to adjust. It’s also clear the European Commission will keep making it as difficult as possible for the UK to agree a post-Brexit trading relationship with the remaining 27 EU member states.

Instinctively bureaucratic, Brussels cares little about trade between the UK and EU. The £240bn of goods and services Britain sells the rest of the EU each year or even the £320bn they sell to us, almost a fifth of the EU27’s total exports, aren’t...