* http://www.paulgraham.com/siliconvalley.html
* http://www.paulgraham.com/startuphubs.html
* http://www.paulgraham.com/maybe.html (a proposed recipe for how to do maybe create a new startup hub; that's actually somewhat more modest than what the tc article describes)
The most salient quote from those articles, IMO: "Of course, a would-be silicon valley faces an obstacle the original one didn't: it has to compete with Silicon Valley."
I would note that if the UK are serious about this "entrepeneur visa" then that could get very interesting. Currently I can't imagine fighting through the federal paperwork required to start a company in California if I weren't already an American. Should this hub nucleate properly I can imagine most non-UK non-US citizens vastly preferring dealing with UK immigration to what has to be a frustrating US system. (Any non-UK non-US folks care to comment more informedly on this?)
And real estate is stupidly expensive in London, so they're halfway to Silicon Valley already.
[Edit: formatting]