Other sources claim that even reverting to WTO status is not a given — see https://www.ft.com/content/5741129a-4510-11e6-b22f-79eb4891c97d
The VW argument (I’ve usually seen it as the BMW argument): this often seems to ignore that the negative effects of tariffs may be on the consumer, not (just) the seller. I think UK is about 10% of BMW sales. That might drop a bit with a tariff, though the exchange rate fall may have a greater effect, which is hardly going to affect BMW’s fortunes. But UK consumers may have to pay more, for the same product. Reciprocal tariffs may concern those like Nissan building in the UK and then exporting to rEU.
The bigger issue may be non-tariff barriers — getting UK exports overly checked at frontiers, for conformance with EU rules, rather than sailing through. So regulatory equivalence is the issue there.
Overall, of course, just means things are really hard to sort out, and to do so swiftly.