Do not believe this is correct. In 2016, London was No. 7, after 6 American cities; it was ahead of Beijing and Shanghai individually, though not collectively [1]. The next European city is Paris, in No. 16, after Chicago, Austin and Mumbai.
[1[] https://www.theatlantic.com/technology/archive/2016/01/globa...
I was slightly off, London comes 4th after the Bay Area, Beijing and New York, but handily wins out over Boston, Seattle, or any EU city.
The business and culture of tech startups is just a really mature and highly developed industry in the US. It started in Silicon Valley but these days it is spread across several cities, and there is more domain specialization by city including Silicon Valley.
Claiming “ahh U.K. is different” you might as well say “ahh Bay Area is different”.
London (like Scotland, Liverpool, Manchester) voted massively to stay in the EU. Other gentrified cities like Leeds, Bristol, Oxford, Cambridge also voted to remain.
Where is your evidence that leave was driven by London doing things differently?
I'll give you places like Stockholm and Amsterdam don't quite hit those heights, but still have healthy ecosystems going for them. But it's difficult to describe the 'EU' way of doing things because the EU is not a federal government; each country is a separate nation, with far more differentiating them than US states