It's not a binary thing. It's not either they work together or they don't.

Under a common block, trading or otherwise, things are just easier and much closer together.

Consider only visas, travel and employment, the complications of these brought by Brexit, already distanced any existing and future collaborations by some measure.

There is still collaboration of course, and there will be, but it's not what it was before.

And this negative trend of distance in collaboration is more worrying in an increasingly threatening environment.