I don't think the Russians have anything to do with it: you must have an old atlas! Baku is in Azerbajan. Other operations in the region are in Kazakstan and Turkmenistan. I would assume that the aircraft would be locally registered and the crews flying either on validations or locally issued licences on the strength of their FAA/JAA/CASA etc licences. Quite apart from any local requirements to do this, the operators of G reg a/c would prefer to get them off the G reg in order to use 'overseas' operating practices, rather than be bound by UK rules. I'm thinking of Flight Time and Duty limits, weather minimums etc.