In message , at 17:09:05 on Sun, 5 Feb 2017,
tim... remarked:
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.

That part is clearly within the SM

Hurrah!

but that is their problem

it isn't a reason why we should be part of, and achieve benefits from,
the CU

Are you now agreeing that the third of the following you listed earlier
is SM not CU:

tariff free trade

ease of customs documentation at borders

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