The revenue custodians earn from foreign exchange transactions is dwindling. BNY Mellon, the world’s largest custody bank, reaped an average of $212.5m in foreign exchange revenue per quarter in 2009; whereas its latest 2012 figures show almost a 40% drop, to an average of $130m per quarter.

State Street's foreign exchange revenue has dropped from an average of $169.3m per quarter in 2009, to $127.8m - a 25% fall.