Compare the interview that Ken Livingstone gets on Andrew Marr (circa 25:00 mins in - also worth watching Jon Simpson on the paper reviews earlier - being biased and then trying to deny it) and what Nigel Farage endures on the Politics Show later (circa 8:00 mins in, with an intro that is less than ...erm... balanced).
Going by this interview presenter Jon Sopel's own views are obvious - his line of questioning is clearly seen to be less to do with holding a politician to account on his policies but more to do with expressing his personal views. I know this is "do bears shit in the woods" stuff but it really is a disgrace.