One of the City of London’s oldest institutions has launched an investigation into whether cobalt mined by child labour is trading on its exchange, following complaints it is allowing a Chinese company to sell untraceable supplies of the metal widely used in mobile phones and electric vehicles.

Members of the 140-year-old London Metal Exchange initially raised concerns about questionable cobalt this summer, highlighting their fears the rechargeable battery material may have come from mines in the Democratic Republic of Congo accused of employing children.

Earlier this month, the LME quietly sent a directive to all suppliers asking them to detail how they guarantee “responsible sourcing” of commodities traded on the exchange. The notice, contained in email seen by the Financial Times, requests a response by December 1.