As a London native for almost 10 years I cant tell you how many times I have been ripped off by black cab drivers taking longer routes then they could have. I also cant tell you how difficult it can be at certain times to find a taxi to take you home so people inevitably end up using unlicensed "mini cabs" to get home. This all because the licensing regulations are stuck in the stone age. Hopefully Uber will drag London kicking and screaming into the 21st century.
As a side note I also dont think there is anything stopping a London black cab driver from signing up for Uber.