Given that US prosecutors are part of the administration, I'm inclined to think that they may have political motivation here.
But why would british politicians get involved. Regardless of how they got involved it would be political suicide if they were caught doing so.
British politicians have very little to win by getting their hands dirty here. For them it would be preferable to tell the Americans that they can't interfere.
Seriously, UK politicians have a perfect excuse for not having to make a choice and take a political risk -- they are not allowed to!
Give a politician the option of passing a hot potato to someone else, and you can be sure they'll pass the potato :)
