Unlike the Editors, I don't believe it is fundamentally unConservative to have all-women shortlists. But there would be profound implications of doing so, flowing from something I do consider to be a fundamental Conservative principle: equality before the law.
Here are three implications of all-women shortlists, in the context of equality before the law. (The first two flow straightforwardly and directly from the principle of equality before the law. The third flows from equality before the law and the principle of liberalism.)
1) Our rulers are subject to the same laws that apply to the rest of us. If a political party is permitted to discriminate in favour of women when it has good cause, the rest of us must be permitted to discriminate in favour of women when we have good cause. If, for example, there is good cause for a company to hire a woman instead of a man, then that company must be permitted similar devices to the Conservative Party (e.g. an explicitly all-women interview list).
2) We must not have discrimination within the law. The law might permit discrimination, but it must not discriminate itself. So, if the law permits political parties and companies and other private agencies/individuals to discriminate in favour of women, it must, likewise, permit political parties and companies and other private agencies/individuals to discriminate in favour of men.
3) The law must not merely permit those forms of discrimination we approve of, but also those we disapprove of, and the law must treat all political parties the same. The only difference between a political party that restricts involvement in certain activities to women and one that restricts involvement in certain activities to white working class people is that we feel tempted to approve of the first and to disapprove of the second. But from the point of view of the liberal social arbitrator, that is precisely the sort of difference that must be ignored. If the Conservative Party is permitted to discriminate in terms of involvement in favour of women, the BNP must be permitted to discriminate in terms of involvement in favour of white working class people.
You either believe in the value of requiring equality of treatment of private individuals, or you don't. I don't. So I'm happy to say it would be genuinely useful for the Conservative Party to use all-women shortlists, and we should also accept (1), (2) and (3) above. But does Cameron? For what cannot be allowed to pass would be for the Conservative Party to employ all-women shortlists, but for the law that applies to our rulers (to political parties) to be different from that applying to the rest of us, for the law itself to discriminate in its treatment of men and women, and for the law to permit only those forms of discrimination we approve of, forbidding those that we (today) dislike.
What's it to be?