If the EU want to retain tariff-free access to the UK they will need to make some concessions
Herein lies the rub: that statement is based on the assumption that the EU wants access to the UK. I'm not sufficiently up in import/export comparisons to know if that assumption is mere wishful thinking or indeed useful leverage in what is certain to be a game of extreme hardball - letting the UK exit without pain in terms of tariffs or red tape would be an argument for others to leave too, at which point the US will have a party.
Why the US? Well, UK's main role as bosom buddy of the US was to prevent the EU become too much of a competing power block in the world. The EU has already caused pain by creating an alternative currency and by telling the US to actually obey some laws (gasp, TOTALLY unheard of concept for a US company operating "abroad"), so UK's pending exit (and associated loss of control) is unhelpful, unless the whole EU goes to pieces.
Having observed the way the US operates in the world I am in no doubt that there are already plenty shenanigans in play behind the scenes to make that happen, or to keep the EU participants squabbling with each other instead of pulling in the same direction (although that was always going to be a challenge with the French involved :) ).
In this context I'm highly amused by the US protesting that the EU acts as "a supranational tax authority that reviews member states" - if there ever was a case of a pot calling a kettle black, this is.