The former Conservative Party treasurer and peer, known as 'Mr Copper' for his $2 billion fund, "is claiming losses related to alleged manipulation of the copper market for three years up until 2013," according to a story run Friday in The Telegraph. The lawsuit alleges that Barclays allowed staff to share confidential information about its positions with LME traders, which enabled the bank to profit by placing opposing bets, according to court documents.

The bank denies it mishandled confidential information. The LME would not comment except to say that anyone in breach of LME rules would be disciplined, The Telegraph said.

Other banks have of course been called to task over alleged manipulation of metals markets.

In April 2016 Deutsche Bank AG agreed to settle U.S. litigation over allegations it illegally conspired with Bank of Nova Scotia and HSBC Holdings Plc to fix silver prices at the expense of investors. Later that year, Canada's Scotiabank (the Bank of Nova Scotia) was forced to turn over internal emails and other correspondence spanning several years. The move was part of a lawsuit accusing four major banks of conspiring for a decade to fix prices and exploit distortions at the expense of investors in global markets for the precious metal.

Investors allege the banks conspired from 2004 to 2013 to fix prices for gold. They did not estimate the size of the banks' bullion portfolios, but said the gold derivatives market alone was as large as $650 billion during the class action period.