The plan involves pumping filtered effluent into the river at Teddington, which the firm says is needed as part of a scheme of works to obtain “a secure and sustainable water supply for the future”.
It comes after Labour and the Liberal Democrats called on Tuesday for an immediate investigation into reports that three major water companies including Thames had illegally discharged sewage hundreds of times last year, even during dry spells.
Rishi Sunak’s spokesman branded the findings from a BBC investigation “completely unacceptable”. But he stressed that the Government intends to strengthen the powers of industry regulator Ofwat and the Environment Agency to go after polluters.
More than 24,000 people have signed a petition opposing the scheme, which awaits a government green light.
Objectors say that with global temperatures rising inexorably, Thames Water could do far more to fix its leaky pipes rather than threatening environmental harm with new works, and are also demanding that it stop fouling the capital’s waterways with raw sewage during heavy rain.
“Thames Water have categorically failed millions of residents right across our area,” Munira Wilson, the Liberal Democrat MP for Twickenham, told the Standard ahead of leading a Westminster Hall debate on the Teddington scheme.
"What’s worse is that this Conservative Government is just so weak and out of touch that Thames Water has been able to get away with this scandalous behaviour for far too long,” she added.
Thames Water stressed that it needed to invest in new sources of water to provide a secure and sustainable supply for the future.
A spokesperson added: “Our work to date demonstrates that the proposed abstraction scheme in West London is a cost-effective option and our environmental studies have shown that the scheme would not cause detriment to the environment.â¯
“The scheme will provide up to 75 million litres per day as a drought resilience scheme. It would only be used during periods of prolonged dry weather.”
Ofwat’s role is also under growing scrutiny.
Gareth Thomas, the Labour MP for Harrow West, has written to the regulator demanding answers as he presses for Thames Water to be held accountable both to its 15 million customers and to the region’s elected representatives.
“Ofwat has treated Thames Water like a favourite child for too long, allowing excessive borrowing to fund dividends for its owners and shocking levels of pay and bonuses for its most senior staff,” Mr Thomas said.
“I am concerned that Ofwat will again turn a blind eye to Thames’ many failings and allow it to use water bills in the coming years to rebuild its balance sheet.”
An Ofwat spokesperson said in response: "Thames Water needs to develop a robust and credible plan to turn around the business and transform its performance for customers and the environment. We will continue to safeguard customers’ interests as they do that."
Thames Water insists it has not paid any dividends to external shareholders since 2017. Its accounts show £37 million of internal payments to its parent company in 2021-2022 to service its £14 billion debt.
Burdened by the impact of rising interest rates on the debt, the board was forced in July to seek another £750 million of emergency funding, after last year tapping up investors for £1 billion.
The announcement sparked speculation the Government would have to mount a rescue, and came shortly after the abrupt resignation of CEO Sarah Bentley. The firm is now under temporary management while the search for her successor goes on.
The capital injection has bought Thames Water time, according to Philip Dunne, the Conservative chairman of the Commons Environmental Audit Committee.
“But the fundamental issues that they’ve got to deal with of creaking infrastructure, similar to many of the other water companies in relation to sewage discharge, remain to be resolved,” he told the Standard.
Mr Dunne said, however, that Londoners should see the benefits of the Tideway Tunnel “super sewer”, which promises to divert 37m tonnes of sewage from the river each year when it enters operations in 2025.
In July, Thames Water was fined £3.3m for pumping “millions of litres” of undiluted sewage into rivers near Gatwick in 2017, killing several thousand fish. Pollution-related prosecutions by the Environment Agency have now led to fines for the company of £35.7m since 2017.
The company insists it is getting to grips with leaks. And interim co-chief executive Alastair Cochran told MPs in July that the utility’s acting leadership was “very focused” on a corporate recovery.
He said: “Our job collectively is to turn this business around.”