He is putting it all on the line!
Clearly the current deal with Eire/Southern Ireland doesn't suit the UK, as it treats Northern Ireland as if it is not part of British territory. Unfortunately, Eire's commercial traffic flows through the UK in order to reach Europe.
So that's a difficulty they have, and I hope we can be constructive in helping them solve it. But it won't work for the EU to hold the UK's sovereignty hostage to a problem which really belongs to the disconnected situation Eire and the EU find themselves in. I don't see the British setting up a frontier. So there's going to have to be a system that tags goods from Ireland, and there will be some level of cheating over tariffs and so on as a result. For me, the solution is to have no tariff barriers between the UK and the EU, but that's just me. Have a common market but not a European Union for countries that aren't interested in being part of a European empire.