A study for the Centre for Policy Studies, a right-of-centre think tank with links to the Conservative Party, has found that the BBC is "biased toward the left" - according to a report in the Telegraph.
Its research has found that "the BBC is twice as likely to cover left-wing policy proposals than those that are right-wing" and "to hail them as “independent” while giving right-wing research a “health warning” by pointing out its ideological position". The CPS has quantified this statement.
The CPS has also compared the corporations coverage through the prism of the Guardian and Daily Telegraph and found that "the BBC covered seven out of ten of the stories on the Guardian, but only mentioned three out of ten reports which had been covered by this newspaper [the Telegraph] over the set period."
This is my kind of statistic thing, so please give it a read. The results tally somewhat with my own tentative forays into this area.