I've never liked Hackney carriages much. As soon as you get in one, you get stuck in traffic. But even if you don't get stuck, one has no idea when one enters the car how much the eventual fare might be. It could be anything!

I live in South London, so in general none of this applies to me, but when I have used Taxis in central London these are among the problems I have faced.

I use mini-cabs every now and then, but I'd much rather use Uber if 'twas available.