I like the way that slipped in there. Is the question of bias undefinable? Or can we define it as "The person who was in charge of editing the BBC's 2010 news coverage went on to be the Director of Communications for Number 10". Or maybe "The presenter of the BBC's flagship toptical debate programme has a history of making factually inaccurate statements about the the Labour party", or "The BBC repeatedly appoints key Conservative journalists to flagship programmes".
I mean, this isn't undefinable, it's very easily definable. For those in the US who may not understand this, imagine you had a state broadcaster funded by taxes, and it had been putting on shows presented by Roger Ailes.
I mean it's really quite basic, people shouldn't be going back and forth from political positions to the independent state broadcast. The state broadcaster should have an open and accountable procedure to deal with factual issues. Neither of those are true, and these systemic issues don't have a neutral political outcome.