Was London at any point the startup capital of Europe? Maybe it was the banking capital of Europe, but that time is over now.
In terms of funding, yes. It's also the fintech capital of the world. Regarding being the banking capital: it's been two business days. You might be jumping the gun just a little. ;-)
I strongly suspect the UK won't be able to continue any passporting[1] arrangements because it would greatly benefit Germany's financial sector if foreign banks had to establish a European presence to trade within the EU. That is an existential threat to London's finance industry. Obviously it depends on trade negotiations with the EU as the UK leaves, but really, what benefit is there to the EU to let it continue the way it is? Why would they want the UK to carry on as it is now?
[1] https://www.eba.europa.eu/regulation-and-policy/passporting-...