Newswatch is hardly a unbiased group. The Express is misrepresenting them to suggest it is. It's a partisan blog that exists to go after the BBC:
http://news-watch.co.uk/ Them 'finding' it's biased is about as as useful as saying The Canary has found Labour are best placed to manage the economy.
They're entitled to their view and argument of course but it's wrong to suggest this was the result of a academic study.