It wont really lose anything. UK can now start new "tax haven" initiatives (discouraged under EU) and companies will flock there better than before...
London didn't get its "preeminent spot in the world of finance" by entering the EU/EEC etc or because of it. It earned that spot by itself 100+ years before...
Not to mention EU is barely doing well itself...
Maybe the one asking had in mind some derelict tax haven islands in the caribbean or so? Not all tax havens are like that...
It has been a global hub for centuries.
This problem gets worse when the past becomes an argument for not taking the necessary steps to mitigate any potential change.
The modern successful UK is almost certainly a consequence of closer collaboration with the EU.
Almost none of the reasons the UK was successful before are true anymore.
Is it? Or just neoliberalism via Thacher making it more alluring to modern capitalism (succesful for society is another thing) and the same cheap credit flood in the 90s+ that happened across the West?