Calling or hailing a cab in London, is just not necessary these days. All those in the know use Uber; a phone app which tracks your location, via your phone's GPS, and connects you to local taxis, quicker than you can say "Taxi for one!".
You set up a profile with your credit card details, so once you have reached your destination, your card is automatically charged. If you're riding with friends, there's even a split the fare option. Cashless and convenient!
It also gives you the option to choose which ride is best suited to you and your budget.
In my experience it is so much cheaper than the cost of any taxi company at the moment. A journey from Camden to Peckham cost me a mere £18! It's an absolute steal.
Enter the promo code "bossit" for £20 off your first ride (valid until 1/11/14)