Black Cabs are licensed safe and during the night it is always preferable to take one. If you find trouble in getting one, you can call a black cab – 02074263420. In the city it is very fast and convenient if you don’t know the exact directions of the location you want to visit. The black cabs are supposed to know all the roads and addresses in the city. they go through a rigorous 5 yrs of probation and tests before they qualify to get a license.
Mini cabs or unmarked taxis are run by private companies and fairly cheaper for long journeys. The best mini cab company in London is Addision Lee (http://www.addisonlee.com/services/minicabs/ 02073878888). They are also very safe, accessible and cheap.
if you don’t get any of them on a weekend night, you can try one of the other mini cabs. But always book from their office. There are many mini cab offices in Central London. If you are leaving a club, you can always request the security to get a cab.
If you are in any trouble, you can dial 999. You will get help in 5 mins if you are in Central London.
London is a great place and I hope you guys will enjoy it. Let me know if you need any help.