"Under EU law, the bloc cannot negotiate a separate trade deal with one of its own members, hence the commissioner's insistence that the UK must first leave."
"It is also against EU law for a member to negotiate its own trade deals with outsiders, which means the UK cannot start doing this until after it has left the EU."
"There are actually two negotiations. First you exit, and then you negotiate the new relationship, whatever that is"
This latter point is very crucial since the UK cannot really be in a position to talk to non EU countries until it knows whether or not it will have access to the single market. If you have access to the single market then you have to apply the EU common external tariffs to other non EU countries there is no freedom to do free trade deals with them end of story.
In addition, there is the distinct possibility that if we have no trade deal with the EU in place within 2 years of invoking article 50 that the EU will be forced to treat the UK as a third country in line with it's obligations under the World Trade Organisation rules. That will mean applying the same tariff to the UK as it does to the US, Japan and China a potential disaster for UK exporters. It would also mean no European passport for UK services (currently UK services firms can sell services into the EU market without the need for EU permission) - for a service sector economy like the UK that would be extremely damaging.
What a fine mess the UK has got itself into!