Definition of Extradition
My reading of the definition of extradition is that it applies to cases where a crime is committed in country A and the perpetrator has fled to country B. In this case the legal bodies of country A can apply to have the perpetrator made available of trial in their jurisdiction.
In this case, by definition, the offence was committed in country B (the UK) so by that definition, extradition to country A (the US) isn't appropriate. But then I'm sure there is a treaty that has words that somewhat muddy that definition.
Hmm, too many definitions,