This is unrealistic bordering absurd, you just came out of Brexit sold under the pretense of increased freedom and sovereignty. The UK didn't even like the special deal it had with the EU, unique concessions that no other country in the Union would get because the Union acknowledged that the UK was worthy enough to be in with those rather than out without them.
It'd be ludicrous to believe that coming from this sentiment the population would agree in joining the US, losing most of its sovereignty to become a 51st State under control of the USA Federal Government, like extremely ludicrous. The cherry on top would be the humiliation to the UK's nationalists in becoming a vassal of a former colony, I don't see this having any chance whatsoever to happen, not now, not in the next 50 years.
I gotta ask, what fosters this hope of yours? I haven't seen a Brit so deluded in wishful thinking as this take, it's a bit baffling, sorry to say.