That actually isn't true:
> As an EU member, the UK was automatically part of about 40 trade deals which the EU had with more than 70 countries. In 2018, these deals represented about 11% of total UK trade.
> So far, 29 of these existing deals, covering 58 countries or territories, have been rolled over and will start on 1 January 2021. The latest deal to be struck was with Mexico on 15 December.