That sets up a game of chicken
Many of the Brexiteers amongst the Conservatives believe they can get a better deal by convincing the EU that they're prepared to go ahead with a no-deal Brexit.
The problem is that it would be a catastrophe for the UK's trade partners but it would be much worse for the UK. It's going to be very tough to get Juncker to believe the bluff but he might get pressure from other EU leaders.