Six water companies in England have been accused of overcharging customers between £800mn and £1.5bn by under-reporting the full scale of their sewage pollution, in a case that could pave the way for bill payers to receive hundreds of millions of pounds in refunds. In a competition appeals tribunal on Monday, lawyers for Carolyn Roberts, a former professor and environmental consultant, accused the privatised companies of abusing their monopoly position to mislead regulators over the amount of sewage they were discharging into rivers since 2015.