Re: Just send him over there and good riddance.
"So what's the alternative, that the UK never extradite anyone to the US because our prisons are worse than UK prisons?"
Yes - that should be the default position, especially for crimes that were not committed by a person on US soil. The US "justice" system is irretrievably broken, the penal system even worse. The UK should withdraw from the disgustingly one-sided extradition treaty immediately so that this situation does not arise again, and think very hard about renegotiation.