It isn't in anyone's interest to tax imports. The UK will not likely get free trade deal, but it'll get a good deal that reflects the above
That's why it was perhaps not the brightest idea of all time to leave the most well-integrated trading block in the world and then try to negotiate a half-baked solution later... You are right, there will be a trade deal between the UK and EU, nobody is disputing that. What is not being disputed either (except by a very small minority) is that it will not be as good as what is currently in place and it will hurt both the UK and the EU in several ways.