Residents and councillors have reacted angrily after the expansion of the controversial Mogden sewage works was given the go-ahead.

Thames Water, which runs the Isleworth plant, reportedly claimed that water and sewage regulators Ofwat would not allow it to cover all of its storm tanks, which is essential for odour reduction.

But Isleworth councillor Phil Andrews said Thames Water did not want to invest any of its own money in tackling the bad smell, and would only take action if Ofwat gave it permission to secure public funds.

The Isleworth and Brentford area committee passed a motion on March 5, “regretting” Hounslow Council’s sustainable development committee’s (SDC) approval of expansion last week.

Coun Andrews said: “The majority on the SDC took a cowardly decision on the back of some highly selective information from officers which is likely to have seriously detrimental effects for residents in Isleworth, Twickenham and parts of Hounslow.”

The motion last Thursday was supported by all five Independent Community Group councillors present and by Liberal Democrat councillor Andrew Dakers.

Conservative councillors Barbara Reid and Sheila O'Reilly and Labour councillor Ruth Cadbury voted against the motion.

Mogden Residents Action Group (Mrag) has launched a legal battle against Thames Water and will apply for an injunction against the operators at the High Court of Justice in October this year.

The group repeatedly urged the SDC to defer the planning application for seven months until after the court’s ruling.

It said this week Hounslow Council had shown an “incredible display of hostility towards residents of Hounslow, Isleworth, Twickenham, St Margarets, Whitton and Richmond” by pressing ahead, and described the SDC meeting on March 4 as a “fiasco, a debacle and a shambles”.

Mrag fears the expansion of Mogden sewage works could cause property prices to fall as “the area becomes a massive cesspool”, and the decision to approve the application could be vulnerable to judicial review because it failed to ensure appropriate public participation.

Solicitor Neil Stockdale, who is handling the group’s case against Thames Water, said: “I fully expect Thames’ expansion plans to be carefully scrutinised by Mr Justice Ramsey at the trial of the residents’ case in October.

“Whether this was the right decision remains to be seen.”

A spokeswoman for Thames Water said: "We are encouraged by Hounslow planning committee's recognition of the need to improve the quality of the Tidal Thames and their positive response to our proposed improvement works.

"It will enable us to fully treat more of the existing flow, significantly reducing the number and concentration of discharges of storm water into the tidal River Thames.

"This will improve the water quality of the river and will reduce the use of the existing storm tanks by 80 per cent. "When the storm tanks are used, the covered tanks will be used first and on the rare occasions the uncovered tanks are used, a cleaning regime, agreed with the London Borough of Hounslow, will be in place to minimise the potential for odour.

"Our prices are set by Ofwat, on the basis of the work they decide we need to do. As the improvement works will result in a significant reduction of the storm tanks being used, funding to cover the remaining tanks has not been secured".