Really? What are you basing that on?
Having worked at FinTechs and in finance in general that doesn't ring true at all. The FCA definitely takes anti-money laundering checks quite seriously.
e.g. (off the top of my head) NatWest were fined £264 million for AML breaches.
I'm no expert by any means but if I wanted to flout the rules I'd definitely consider a few other juristictions before the City.
AML tech is so primitive, it almost looks like it's designed that anyone 'in the know' will know how to not be detected.
Eg. Most AML checks are done because someone wrote some triggering keyword in the payment reference field. Do we honestly think a criminal mastermind won't manage to come up with something else to write there?