I'm nearly at the point of saying that a tobacco sales isn't the best analogy here.

I could be milk, right? Or a sheet of paper.

I'll concede that it's not terribly far fetched. If the french entity produced a good that is illegal in the UK put it in the post to be delivered to the UK, then we have something like an analog to producing HTML in one place and displaying elsewhere.

However, the thing about sovereignty is that you don't have it if you can't enforce it.