[wisty]

Unfortunately, London and Berlin are national capitals. Silicon Vally (even if you extend it to San Francisco) isn't even a state capital.

National capitals have defence contracts and government IT, which so lucrative it sucks a lot of talent away from industry. London is also a financial centre, so that's even more competition.

[justincormack]

London does not have defence contracts, thats largely out west, Reading way. It does have a fair amount of government IT, but that is more dispersed too (uk.gov is a new exception, but historically things like tax collection were moved out of London back in the 1970s).