> This isn't some one sided negotiation.

This is pretty reckless risk management on Britain's part: to place so much weight on a question of just how a future, unclear negotiation, subject to who knows what bureaucracy and other countries' own interests, will turn out. It's very vague to just say "well we're trading a lot, so surely we're very important" without any supporting evidence or precedent: it makes all sorts of unjustified assumptions.