If you are visiting London and you need a taxi ...

[whitedesire]

... try Uber, it's brilliant. You register your details including a credit card, use the App to flag down a Uber cab and bob's your uncle. On the app, you can see the cabs on a small map in the area, you can see them on the map evening driving around, brill. And cheaper too and the cars are excellent, clean roomy etc. I think Uber are in other cities also in the UK.