The world’s biggest precious metals exchange says it is taking the latest allegations swirling around the Perth Mint very seriously as the West Australian government stonewalls on calls for a royal commission.

The London Bullion Marketing Association (LBMA) announced on Thursday that it has launched an investigation, known as an incident review process, into the WA taxpayer-owned mint amid allegations it tried to cover up the sale of less than pure gold to the Shanghai Gold Exchange and only stopped the practice after its biggest customer complained.