Yeah, there's a lot of them about, particularly in areas that the black cabs don't like to serve (such as where I live in South London). Fortunately, I've got a very good local minicab company (their only annoying feature is turning up too early for airport runs, when I'm still in the shower ), but otherwise... You're stuck with what you can get. Clapham Junction, Clapham and Brixton are particularly bad for this.

I've taken them a few times, in groups, and they've been fine. I would never get in one alone. Wherever I am in the world, one rule applies to taxi journeys: only ever get in one you've asked for yourself. If they approach you, the chances of a rip-off (or worse) tend to be greatly increased.

The situation's not as bad as some other places. Amsterdam, for example, allows any old mupped to stick a 'taxi' sign on the roof, and charge pretty much what they want. There are (or have been) 'mafia' operations outside several major hotels, and sweeps at Schiphol have uncovered a scary amount of firearms in the taxis. JFK is pretty bad for touts, as can be Roissy at times. The good thing about the London situation is that you can see exactly what you're getting. A black cab is a black cab, a reputable minicab is something else, and a 'gypsy cab' something else entirely.