In message , at 14:04:17 on Sun, 5 Feb 2017,
tim... remarked:

"country of origin" rules for "supply chain" industries (Automotive
being the most important example)

My understanding is that's a Single Market thing, not CU.

Then your understanding is wrong

I don't think so. The kind of rules you refer to are presumably "if it
meets EU standards in one country, it will in another".

Post-your=Brexit there's nothing to ensure that while the customs people
will let the stuff in, without a tariff, that the customer will
automatically discover it meets the standards.
--
Roland Perry