In the FT, Paul McClean reports that according to FT estimates and as a consequence of Brexit, the UK will have to negotiate more than 700 treaties with third countries. More than 160 countries need to be dealt with; Switzerland, the US and Norway stand out.
Some negotiations have to be concluded very soon:
… the EU-US Open Skies accord for airlines, were agreed when the forces of liberalisation were at their peak. The political mood has hardened considerably since then. … The timing is tight. The US needs to know the UK’s arrangements with the EU before it can commit, and that may not be clear until late 2018. … “It is not as if you can wait until March 2019 to see what the regime will be. You probably need clarity by the early summer or spring of 2018.”