Because it is so fundamental to the British establishment's sense of British identity, the BBC can hardly be expected to offer impartial coverage of the Scottish independence referendum, although their coverage of events in Russia would probably be quite fair and balanced because they have no axe to grind.
And the same is true in reverse. Russia Today exists to portray a favourable picture of Russia to the world, and what it says about Russia has to be seen in that light. But its coverage of events outside Russia seems quite fair and balanced. Watch this Sophie Shevardnadze interview with Alex Salmond and judge for yourselves. It's one of the better ones I've seen.