Craig Donohue, chief executive of the CME Group, the US futures and options giant, has defended the exchange’s decision to raise margin against commodities traded on its platform and has rejected claims the CME was responsible for a sell-off in silver futures.

Silver futures plummeted 27% in the first week of May, following margin hikes on the CME's commodities trading platform. It was the biggest weekly plunge in silver prices since 1975 and followed an 84% increase in the amount of margin the CME demanded to be posted to secure positions.