Here is thread with few facts relevant to current drama on Brexit deal or rather more likely NO DEAL - FOR NOW!
1.) If we have to go to ‘no deal’ (/Australia deal) we will be doing what most members of World Trade Organisation (WTO - covering virtually every country in world) do.

2/ 2/3rds of trading in world is done under WTO rules. USA exports more than UK does to EU but does so under WTO rules; so does China.
2.) If tariffs have to be imposed under ‘no deal’ WTO rules, the EU will pay £12bn in tariffs a year and the U.K. £5bn (ref: Civitas) -

3/ (ref: Civitas) - because tariffs hit mostly agricultural EU goods, such as 40% on cheeses & 12% on wine;
3.) The £12bn income from tariffs will come to UK Treasury, not Brussels. Effectively these will be UK consumer taxes that could perhaps go towards reducing COVID debt?;

4/ 4.) 43% of UK exports do yes go to EU; but this is small proportion of our actual economy: only 7.5% UK GDP are goods exports to EU; 13.5% with services. Only 8% UK companies even trade with EU. (@BBCNews please show balance on this). Most of our trade is internal within UK.

5/ over 2/3rds (SNP take note!); so tariffs will effect a small proportion of UK exports (though some sectors will be hit hard;
5.) By definition, 57% of U.K. exports go to Rest of the World. Growth outside of Europe is forecast to be 90% of all growth over next 15-20 years.