Nick Clegg has published his second Brexit briefing paper. This one looks at what Brexit means for Britain's international trading relationships. Whatever your view on Brexit, it makes a good primer on the many complex issues involved in unpicking our current arrangements.

Those of us who regard Brexit as a disaster will be reinforced in our views by passages like this:

If we sign an FTA with the EU, or seek to adopt a Norway-style relationship, then British exporters will also have to comply with complex ‘rules of origin’.

These rules require UK exporters to obtain proof of origin certificates from their national customs authorities to guarantee that the product (or an agreed percentage of the product) originates in the UK. 

Under an FTA, goods have to be shown to come from the country in question in order to benefit from the preferential tariffs agreed under the FTA, and to prevent third country imports from being passed off as domestic products. These rules are not applied to countries inside the EU Customs Union. 

The economic impact of rules of origin has been estimated to increase trade costs by between 4% and 15%. The impact would be particularly pronounced on companies with highly integrated cross-border supply chains like the British aerospace and automobile industries.