It says regulator Ofwat may have allowed water companies to discharge waste into rivers outside of exceptional circumstances.
The Office for Environmental Protection claims ‘misinterpretations of some key points of law’ may have allowed it to happen more often.
Munira Wilson, MP for Twickenham, said:
“The lack of proper scrutiny and transparency when it comes to dumping sewage into our precious waterways just beggars belief.
“In my own Twickenham constituency, residents have been fighting controversial proposals to pump millions of litres of treated sewage into the river at Teddington since January. We’ve questioned how people can be expected to trust the government and water companies given their record, and now the environment watchdog is questioning it, too.
“Enough is enough. This just adds more fuel to the fire that the Teddington proposals should be stopped in their tracks.”
Thames Water says the plans are necessary in order to cope with demand after 2030.
Twickenham MP Munira Wilson led a debate in Parliament last week to challenge the Minister for Environmental Quality and Resilience, Rebecca Pow, on Thames Water’s Teddington Direct River Abstraction proposals.