There's other women-only cab services in the UK - the one I know of is Ladycabs in North London, which has nearly all women drivers ("nearly" because the boss's husband is also a driver - but you can specify you don't want him!), but which will take both men and women, and, crucially, unsupervised children. I agree with the comments above - they aren't a solution to the core problem, but they are useful in the interim. (And here I go, being all optimistic, using words like 'interim'...)

There's also a, hrrrm, very difficult ad poster campaign all over London at the moment, by Cabwise, the government cab licencing authority, warning women not to take unlicenced cabs. Basically it's panicky text and a close up of a woman's face as she's being attacked (if anyone googles it, use caution as it could well be triggery, and there's a Cabwise video ad from a couple of years ago, which also comes up on google, which is nigh-unwatchable for the same reasons). I can see what it's trying to do, but it's very much a "don't do this or you might be raped" ad, placing the onus on women to avoid particular situatuons, when I've yet to see a Cabwise "guys - don't rape women" ad.