As someone who has lived here for 6 years or so -- it is pretty rare to work with people who are actually from here -- the tech scene here is mostly people from outside london, or from somewhere in europe, or somewhere else... There's a rather big financial draw (we have some of the highest day rates in the world)...

Whenever I meet/hire a real londoner, though, they do get the "So you DO exist!!!" treatment for a bit ;)