Given that Northern Ireland is effectively in the EU trade-wise it would make sense for UK to put most of the southern UK into the same state for frictionless t

Given that Northern Ireland is effectively in the EU trade-wise it would make sense for UK to put most of the southern UK into the same state for frictionless trade with the EU, but have areas of the UK that can free trade with the rest of the world. Would mean an internal "border" say from The Wash to the Bristol Channel. Effectively there would be two classes of goods - EU and non-EU - subject to different rules. Or maybe the border could be horizontal - a non-EU layer able to free trade with the rest of the world, and an EU-compliant layer on top. Goods would stay in their own layer unless they cross the non-physical border in some computer system someplace.