UK is outside of tree trade agreements with the Commonwealth (Australia, Canada, etc.) because of its free trade agreement (i.e. EU) with collapsing eurozone. That's not good business for them.
Well the CETA (Canada EU trade agreement) with zero tariffs and improved labour mobility is close to being settled by the sound of it. It is not clear if the UK would ever manage to negotiate to join NAFTA.
I don't understand people who think a trading nation can survive outside a free trade area either.