AOG
I think we need to be clear on positive discrimination. It happens all the time and it happens across racial, religious and gender lines.
If I were interviewing two candidates for a position on my team, and one was from an upper middle class family, went to private school and the to Oxbridge, and the other grew up in a one parent family on a rough estate...if both of them were equally qualified, I would most likely pick the housing estate kid, because I know that the other candidate has a much greater chance of success in life, because there are no barriers to him (or her).
However, counter to that, I'm not convinced by positive discrimination generally. It's a poisoned chalice.
In the example I gave on two job candidates, they were equally skilled...but that never happens in real life. You never get two candidates that are exactly alike in abilities.
If the 'housing estate candidate' were less skilled than the 'Oxbridge candidate', then he wouldn't get the job. Same goes for race. Whoever is best wins.
What we need to be really careful about is thinking that the Conservatives would elect a leader primarily because they are black or Asian. That's not what this is about...it's about numbers. Cameron is saying that numerically, the Conservatives have the most black/Asian MPs, so it's fair to say that the first black or Asian PM will be a Conservative.
I think that's slightly muddle-headed (there are a lot of other factors to consider), but I understand what he's driving at.