A lot of international trade is other goods. Think of how much the UK has paid for things like American aircraft, ships, machinery, or materials used in manufacturing. Our armed forces use a lot of American stuff, and often even British made things have American parts (and a lot of it is covered by ITAR, to an even greater extent than the rest of Europe).
People also tend to hugely underestimate the amount of British manufacturing for the same reason, and because of lot of it is Foreign branded (e.g. Nissan cars).
So I fail to see why I need America at all...
Ah, yeah, one big exception: my computer. Argh!
So you would be happy for the Russians, the Chinese etc. to be able to overfly the UK and send ships into UK waters at will?
You want all the factories using American made machinery, or American inputs to close?