The US Federal Energy Regulatory Commission (FERC) has said Barclays and four of its power traders must pay fines totalling $453m (£300m) in its most ambitious market manipulation case to date.
The record fines, first proposed by the regulator's staff in October 2012 over alleged manipulation of California and other western power markets by the British bank last decade, were upheld in an order after assessment by FERC commissioners.
Earlier findings by regulatory staff said the bank deliberately lost money in physical power markets to benefit its financial positions between 2006 and 2008, and that the Barclays traders knew their activity was unlawful.
More top news
A comedy drama series which details the lives of Russian expats in London will air tonight.
A 65-year-old man was attacked by a shark in Australia on Friday, leaving him with serious leg injuries.
Nearly one million people could have their homes repossessed because they do not have a plan to pay off their interest-only mortgages.