The cia in london during the bourne ultimatum

Does anyone know whether the CIA (or NSA) is really as omnipotent as it's portrayed in this film?

From watching the news in Britain, it seems that our police, or MI5/6 can't do a thing without a major media uproar and shouts of human rights, yet the CIA seem to be able to abduct our citizens off the streets and gun people down in crowded stations.

I'm guessing this is all just fantasy, if not, I'm going to be watching the CCTV cameras more closely when I'm catching a train from Waterloo.