Rule of law (and separation of power) does not exist => Berezovsky was allowed to live in Britain over Russian objections due to specific orders from someone important => that important person likes Berezovsky (or perhaps finds him instrumental in his plot to destroy Russia) => since he controls all aspects of British society (like the mainstream press, the Scotland yard, the courts, etc) and likes Berezovsky, he is not going to let Sc.y. to investigate him -- pretty logical, once you make a few assumptions, no?