The UK is perfectly happy to leave trade tariff-free and not link it with all the rest of the EU bullshit. If the EU isn't prepared to do so that is their prerogative but one which they have to take the responsibility for.
There is no causal link between free trade and settlement rights they don't have to be paired.
There is a causal link, you need to respect the same rules and not create a disloyal advantage by for example reducing taxes or wages to ridicule figures. If the leavers are true to their word, they don't want to respect the market rules and want to make their owns.