And if the UK wants tariff-free access to it after the transition period transpires -- as was Johnson's position last autumn when he struck an initial Brexit deal with the EU -- then the EU will need it to sign up to those rules.
This level of insouciance is not uncommon across the EU's institutions, where an official working on the negotiations said with a shrug that "the UK is free to do whatever it wants" and that Brussels is prepared for a "stalemate" at the end of June.
So if Boris Johnson is serious about wanting to avoid no deal, the combination of the talks being frozen, both sides being distracted by a pandemic and this pressing June deadline makes for a hellish start to the summer.
The UK is due to exit Europe's trade and customs arrangements at the end of 2020, despite growing pressure from business groups and opposition political parties to extend the Brexit transition period.
Anand Menon, director at the UK in a Changing Europe think tank, said he didn't think there would be a breakthrough during this week's talks, despite it being the last full round before a crunch meeting later this month, where both sides will take stock of progress.
The UK in a Changing Europe's Menon said that while a major breakthrough in negotiations was more likely in the autumn, so was Prime Minister Johnson taking the nuclear option and deciding to walk away from talks altogether.