Custodian banks in the US are facing up to a world in which they have to hold capital against what they see as riskless assets – deposits placed at central banks – after the Federal Reserve finalised details of a surcharge that will apply to global systemically important banks (G-Sibs).

With custody deposits growing and margins shrinking, industry critics claim the added capital requirement could prevent custodians acting as a safe harbour in a future crisis.

"This is a problem for the entire