EU is more than just a trade agreement and there is nothing preventing trade agreements between the UK and the EU from being developed post-brexit.

1st of November, Boris (or whoever is PM then) asks EU for trade deal. They respond with, "great, so about:

1. Irish border and Good Friday agreement

2. EU Citizens rights in UK

3. Payment of billions to which previous UK governments signed up to as EU member

4. How will you ensure low quality food from US does not enter EU"

This is how international trade works. It's intimately intertwined with diplomacy and each party will play according to its own interests, related or not.

Just like Russia could say "no gas for you" if you make too much of a fuss about what happened in Crimea.

Now if the UK's view of its own future diverges from the EU, it's totally normal to see complications appear during negotiations.

After leaving, the UK will be in a weak negotiating position. Recession is almost certain, and even using an existing trade deal like CETA as a basis will take multiple years to negotiate because of the current UK red lines, like controlling their own immigration policy.

Canada had to adjust their immigration policy for several EU countries to get CETA. The UK will be over a barrel and will have to make major concessions.

Whether you're pro EU or not this situation is a total balls-up.

Exactly. This is going to go extremely badly for the UK.

Watching the UK negotiating a trade deal with the USA and China at the same time, considering the current geopolitical climate, will be outright interesting. Also take the HK situation into consideration.

Hard to imagine a good outcome.