My favourite measure of bias across the Beeb is the super-average interruption coefficient - which is calculated very simply by adding up all the individual I.C.s for each party & then dividing them by the number of interviewed granted to each party that month. As with all statistics, the larger the sample, the better the result (with the consequence that the Sinn Fein figure, based on 2 interviews, is probably not typical!) - and more significant any differences (hence the increase of the I.C. to 2 decimal places).
Here is how things worked out in October 09:
Conservatives (124 interviews) - 0.87
Sinn Fein (2 interviews) - 0.75
SNP (11 interviews) - 0.65
UKIP (4 interviews) - 0.60
Labour (134 interviews) - 0.54
BNP (2 interviews) - 0.50
Greens (2 interviews) - 0.45
Liberal Democrats (32 interviews) - 0.37
Plaid Cymru (2 interviews) - 0.35
DUP (2 interviews) - 0.15
Alliance (1 interview) - 0
Now here's some strong statistical evidence that the BBC, as a whole, is significantly more likely to interrupt a Conservative spokesman than a Labour spokesman, not to mention a Lib Dem.