Seem to recall in a Shephard Press Defence Helicopter article or two between 2004 and last year there was mention of RAF and USAF sending some crews to train on MI-17 .
Maybe the MI-17 are used for test and evaluation purposes for the TPS Rotary Wing Courses for there's a part of the course of evaluating and giving presentation other types of a/c outside. They call it preview course or something like that.