Let's take the forthcoming budget as a topic.
In a balanced report would get the news item followed by a comment from the Cons/Lib Dims and another from Nu Liebour and then if applicable and time allowing a comment from the public with say two pro Tory and two pro Labour.
However I've noticed of late, as I I have so often in the past, that the sequence has been - News item critical of Coalition policy which contains a comment from the Chancellor and then as balance an interview with Balls who is allowed to spout uncontested that there is a Cost of Living crisis, that Labour will be fairer, tax the rich and generally lead us to the promised land.
Keep this in mind when you watch a news report and see if I'm not right.
This is of course political bias in favour of the left.