It is still a barrier even just by being different. The British drive on the left side of the road, all domestic manufacturers make cars which are left side dri

It is still a barrier even just by being different. The British drive on the left side of the road, all domestic manufacturers make cars which are left side drive. If you are from the majority of the world which is right hand drive, you can't just directly export your default car in bulk to the UK and expect it to sell. This makes it a barrier to imports into the UK, and also exports from the UK. It is a non-tariff barrier to trade. EU and US egg safety rules are mutually incompatible.