[pjc50]

EU exporters will have to abide by British regulations (without any input) if they want to sell products to Britain

Market segmentation applies.

At the moment, if you want to sell a product to the 'west', depending precisely what industry you're in, you need (a) CE marking for the EU AND (b) UL or similar approval for the US. That's two sets of certifications, which can share some but not all lab reports. There are then sub-modifications required for the UK: left-hand-drive cars, BS1363 plugs, etc.

If the UK starts to deviate from that such that CE marking is no longer sufficient, then we're likely to see either manufacturers not bothering or just passing the extra compliance costs on to the customer.

This is before you get onto the question of trade in services, such as the UK's major financial services industry.

(I'd argue that the big undemocratic TPP, TTIP, and WTO agreements are more of a sovereignty impairment than the EU, but that's not a view with much traction)