From the BBC:
As an EU member, the UK and UK-based firms can sell their goods to EU customers without having to pay additional taxes. Likewise, British firms and consumers can import from the EU tariff-free.
The prime minister has already ruled out continued membership of the EU's single market post-Brexit, with many assuming this means the UK will also leave the customs union.
So what will we do instead? Essentially there are two options:
◾ a newly negotiated trade deal like the EU has with Canada or South Korea, which eliminate most tariffs and many other trade barriers. But the EU's record is one of slow progress in similar talks, and political tensions from the Brexit process could also be an obstacle
◾ an arrangement sometimes called World Trade Organization (WTO) terms.
What about the third option? The UK declares unilateral free trade and abolishes all quotas and import tariffs, that requires no haggling whatsoever, if other countries want to be prissy and impose quotas and duties on UK goods and services, that's as can't be helped.
If I were 'negotiating' with the EU, I would point out to them that our starting position is unilateral free trade with all comers; if the EU is not happy with that, we're prepared to compromise and declare unilateral free trade; and if that is not acceptable, we'll just walk away and declare unilateral free trade. What time's the last Eurostar back to England?
To be fair, the idea gets a mention later in the article:
Some economists, including Patrick Minford of Cardiff University and one of the leading members of Economists for Brexit (now renamed as Economists for Free Trade), favour a more comprehensive exercise in cutting tariffs and other barriers unilaterally.
But these cuts would have to apply to goods coming from the EU as well.
Well of course they would, that's the whole point.