Off the top of my head; UK startups that have grown and been successful (although many have now been bought out - which I guess is the exit plan for many founders anyway)

Just Eat, Deliveroo and The Hut Group; Monzo, Starling and Revolut, from another era, there's ARM.

I'm sure there's fintech ones (not a sector I know much about) and the guy who sits near me in the office, who has an AI-healthcare startup, says the Britain is very good at those too.