1. Trade with the EU is still possible, it’s just much harder to do. Unless the PM is Truss levels of thick, he would make a deal with the EU.
2. If the US tries to blockade the UK, that would be Article 5 worthy, hence, War with two nuclear powers.
3. Even if we ignore that: Attacking shipping between the UK and the outside world would also include attacking friendly or neutral countries, including EU and NATO members, because the channel is one of the busiest shipping lanes in the world. Hence, bad idea for America.
4. The Channel Tunnel (the Chunnel) allows for freight trains to pass between the UK and mainland Europe.

In short: If the US tries to blockade supplies between the UK and the rest of the world, be it by Sea or Air or Rail, the US would still be at war with NATO and the EU, as well as many other countries (the countries of the ships that are attacked for example) because the UK doesn’t merely have a lot of allies, but they also get a lot of shit from the same routes the UK does.

Yes, a second NATO member on the list and one with Nuclear Weapons operating on a deadman’s handle. I’m sure that’s wise.

The only way she is going to force the UK into using that stupid name is if they invade and conquer the UK.