The London Metal Exchange has discovered bags of stones instead of the nickel that underpinned a handful of its contracts at a warehouse in Rotterdam, in a revelation that will deliver another blow to confidence in the embattled exchange.

The amount of metal represents just 0.14% of live nickel inventories on the LME, worth about $1.3 million at current prices, so the immediate impact on metals markets is limited. But the shock announcement has much wider implications: in an industry riddled with scandals, the LME’s contracts are viewed as unquestionably safe.