You did ask...
The customs union is (thankfully) much simpler to explain.1/
The customs union is (thankfully) much simpler to explain.1/
EU member states make two key commitments on customs. First, not to levy customs, or charges having equivalent effect, on goods from other member state by reason of the fact that they cross frontiers. 2/
And second, they have a common external customs tariff. The member states have afforded significant powers as regards the EU's external trade relations to the Commission, which is responsible for negotiating with other countries (and trade blocs). 3/
If the UK is outside the customs union, one consequence is that goods from the UK/EU may face tariffs when entering the EU/UK. The extent to which this will be the case will depend on the terms of the future relationship deal (and on WTO rules). 4/
A second, is that the UK will set its own customs policy. It will lose the benefit of deals it has as an EU member state. It will be able (within the confines of WTO rules and the new political environment) to make new deals. 5/
Perhaps the key point is that the customs union deals only with tariffs; ie charges. It does not deal with issues of regulatory divergence. Those are dealt with via the single market. 6/
If the UK leaves the single market there will be a need for regulatory checks at borders ('friction'/'infrastructure')... whether or not the UK remains within the customs union (which would eliminate only tariffs). 7/7
