Nothing shakes things up like a systemic shock. The global financial crisis, the 2015 Swiss franc de-pegging and the 2018 collapse of the GTEC Pandion hedge fund have each in turn contributed to foreign exchange prime brokers cutting ties with scores of less creditworthy clients.

Now, some of this business is ricocheting back to them via so-called prime-of-prime (PoP) brokers, which allow clients shunned by large banks to trade through their accounts with some of those same banks. And not all