Guardian: Growing concerns about the accuracy of prices reported in the natural gas market have been underlined after three major brokers launched their own set of indices covering the UK and Europe based on confirmed transactions. The "Tankard" benchmarks have been created by ICAP, Marex Spectron and Tullet Prebon, and come in the wake of an investigation into market pricing and reporting by two of Britain's top regulators following Guardian revelations from a whistleblower. The new indices are believed...